First I was thinking of how these two worlds could connect. I got two solutions:
1. Xiang Fei knew TGCF's author and had helped them brainstorm and write the novel.
2. It was one of his earlier novels that didn't get popularity.
So either way, when the system was creating the world for PIDW, it pulled TGCF and the Heavenly Realm along to answer and fullfil a very important plot hole: What happens to immortals after they ascend? And it also conviently filled the plot hole of Heavenly Demon's origins, something that wasn't discussed beyond a few throw away lines in PIDW. (COUGHS this is definitely not something personal I'm bashing my head over but anyways).
Both of these stories take place simultaneously, but neither realise the other's presence because they were too busy with their own problems.
Eventually, the story ends in TGCF and Jun Wu is no longer the heavenly emperor. Now the question is, who will take his spot?
Shi Wudu? Unfortunately, the god who was next in line is dead.
Xie Lian? Unfortunately, the god who defeated Jun Wu refused to take his place.
Pei Ming? Are you an idiot? Horrible suggestion!
Eventually, they decided to ask <insert some plot device by either PIDW or Jun Wu's swords>
And who does said plot device point at? A pathetic little hamster who has somehow cultivated to immortality.
At first, they're dissapointed. But the closer they look, they more they realise he's perfect.
Someone who can manage and organise tasks efficiently, is looking after two different ecosystems with totally different politics at once and is the sole reason why they aren't crumbling, he's a human and yet the second more terrifying person in the northern kingdom's court, knows a LOT about politics in general, etc.
But the most important part: he's the reincarnation of the creator of this world??
Okay, they're convinced he's perfect.
The gods pull some shenanigans to help Shang Qinghua ascend early, to the dismay of everyone in Cang Qiong Mountain and the Northern Demon Realm.
Queue a VERY freaked out Shang Qinghua who was overworked, but still living a pretty good life suddenly finding out the heavens have decided he's their new ruler.
WHEN DID HE EVEN WRITE THE HEAVENS INTO PIDW????
He does everything in his power to try and escape, only to find out it's futile. He's a god now. Gods also have rules.
So now he has to wait until his king comes and saves him. Somehow.
He trusts Mobei Jun to do that.
However, in the meantime, he realises just how bad conditions are in the heavens. These so called gods do NOT know how to take care of their own home!
So, he decides to help around a bit and started fixing things. (What? He's getting bored. Besides, these people might have kidnapped him but they still treat him really well.)
Ling Wen is too inefficient? Pah! He's heard about that one! Every god is now forced to appoint generals in their own palace SPECIFICALLY for minuscule paperwork. The only time they're allowed to bother Ling Wen is when the matter is big, involves other gods, or they require assistance.
The gods are slacking instead of doing their jobs? Let's introduce them to the system of punishments! Shang Qinghua didn't appoint anything too evil or horrendous, but it was annoying enough for the slackers to focus on their work instead.
The Marital Gods of the South are always fighting? They now have rules that force them to work together in a way that handles all the problems, and requires minimal assistance from the other person.
He also rebuilt the heavens and did away with most of Jun Wu's rules — especially the ones that didn't make sense — and replaced them with his own that gave the gods liberty while making sure everyone was still being productive.
It's a win-win situation for all! Shang Qinghua's teacher is shedding tears of joy and bragging about his position to everyone. (Shang Qinghua lets them. I imagine these two to have a good bond).
Meanwhile, in CQM and the Northern Dessert, everything is chaos. They hadn't realised JUST how much Shang Qinghua managed until he was gone.
They didn't know what happened to him, just that one day he was covered in bright light and ascended in the sky. Shen Qingqiu would describe it as him being kidnapped by a UFO, cuz it looked just like that!
It takes them a good amount of time to conclude that Shang Qinghua had an early ascension, because usually, all Peak Lords are supposed to ascend together through a fancy ceremony.
No one makes peace with this. Especially not Mobei Jun. The Peak Lords could have tried, but they refused once they realised that their Sect was falling apart.
Through Luo Binghe, the two ecosystems decided to form a temporary alliance until they can get their hamster back.
When they eventually manage to invade the heavens, what they see is....
A perfectly working civilization, which has the hamster man in it's centre, working as their emperor and taking care of the entire heavens.
....They definitely had not expected that.
Shang Qinghua is dismayed, and still very happy!
He's glad that his king eventually managed to find him, but....
He doesn't wanna go? Not anymore? Being in the heavens had been really fun for him. Sure, he knew the gods just wanted him to handle the tough jobs, but they treated him with respect. He was above all of them. He had his OWN palace, instead of working as a Royal Advisor in one, for goodness's sake!
But at the same time, he missed his King. He really wanted to go back. Before his sudden ascension, Cucumber-Bro had told him that Mobei Jun was trying to court him the demon way. Marrying his ideal man is living the dream!
But.... It's so fun being at the top, for once! With people that laughed with him and invited him to everything! He's made so many friends! Before, Shen Qingqiu and Mobei Jun were his only friends.
Wait, are his disciples okay without him? Didn't he just dump them with all his responsibilities when he left? IS THE SECT OKAY? Won't there be assassination attempts on Mobei Jun, that he can't foresee for him?
Shang Qinghua just wants to work for all three places at once, but every man has his limits. He knows he's not capable of that, heavenly emperor or not.
I didn't think of how this gets resolved but anyways
I like to imagine Shang Qinghua and Ling Wen making great friends. Ling Wen can't go back to recieving prayers and being a regular god herself, because of the brocade and everything. But she was still a VERY important aspect to the heavens. And Shang Qinghua personally related to her a lot.
So he makes Ling Wen HIS Royal Advisor, and her palace becomes an extension to his own.
She's fine with this. Shang Qinghua had not stripped her of all of her powers. She still got access to all the information coming in the heavens. And guess what? Her workload is reduced! Less stress is very healthy for her.
The only disadvantage? She doesn't have the same freedom as the other gods. But she can get used to that. It's better than being a prisoner who does all the paperwork without anything in return.
Shang Qinghua and Ling Wen often drink together while they gossip and roast the other gods behind their back. Everyone they've every known is a headless chicken running around aimlessly without their assistance!