there are huge changes regarding Guardian Cats in the AU, that i want to address
they of course still live in the city, in the church, but how clan cats meet them is very different
when Darktail raided lake territories, his group attacked WindClan right away and killed few cats (including Whitetail). the moment Onestar saw him, he called retreat and survivors ran towards ThunderClan territories (some were unfortunately captured, including Kestrelflight).
Darktail wanted to get Onestar, but since he and remaining WindClanners hid in ThunderClan (which was a big clan), he decided to wait. and because WindClan’s camp was in the open, he wanted better camp. so they raided RiverClan.
see, this entire time ShadowClan had closed their border - Russetstar ruled it pretty iron claw and didn’t want them get too much involved with other clan affairs anymore. she believed it was for the better, after Great Battle. Tawnypelt (her deputy) didn’t really agree with that, but that way they had more authority and power over their apprentices (which rebelled anyways, but this time because ShadowClan was too strict with rules). so RiverClan was practically in the open for an attack, due to WindClan being taken over and ShadowClan closing their borders. Darktail captured plenty of RiverClanners, including Mistystar, Reedwhisker and Willowshine, while the others tried to seek shelter within ShadowClan
even with Mothwing’s presence, they were turned away and most scattered in panic - wandering far away the clan territories, eventually running into the city and Guardian Cats
Mothwing and very few made it to the ThunderClan, but by the time Darktail’s group had almost as many rogues as ThunderClan, and ShadowClan didn’t want to help.
imprisoned Wind and RiverClanners, along with few ShadowClan apprentices-turned-warriors eventually fought back, when Darktail was away to kill Violetpaw, and then ran away to the ShadowClan. despite Russetstar initial unwillingness to help, seeing how badly the survivors were looking (and well.. Mistystar was still there) and how much power Darktail gained, she decided to aid ThunderClan in fighting him off. SkyClan also arrived, yadda yadda
so knowing the background of how RiverClan met Guardian Cats, after Darktail was killed and his rogues scattered, remaining RiverClanners were still sheltered by ShadowClan, due to their damage, camp being ruined and Mistystar recovering from losing most of her lives. she was whiskers away from losing her last one and merging RiverClan with ShadowClan, due to the loses and clanmates missing - but Reedwhisker wanted to go and find the missing ones.
after receiving a vision of a big, shining building, he left ShadowClan camp and started his search. same night Willowshine and Crowfeather tagged along, because.. ‘dude you are next in line to lead RiverClan, your mother is losing her mind, where the fuck are you going’.
they found Guardian Cats and missing RiverClanners and after few days, they decided to go back - some cats decided to stay back, but others wanted to go back to RiverClan. same day ShadowClan’s camp was raided by ex-Kin, including Sleekwhisker, and they managed to kill Russetstar (she came back) and Mistystar (she didnt). sheltered RiverClanners obviously freaked out bc they didn’t had a leader or deputy OR medicine cat (other than Mothwing, but she didn’t want to lead nor appoint anyone).
during the way back, Reedwhisker got run by a train, while trying to help Duskfur, and instead of burying him, Crowfeather and Willowshine decided to take him to Moonpool and baptize him anyways. Duskfur and Jayclaw tagged along. Minnowtail took the others back to the ShadowClan camp, where she announced that their deputy is back and is going to get nine lifes (totally skipping the part where he got smeared all over the train tracks).
soooo. yeah. Guardian Cats are still there, but none of them are taken to clans and are let alone. those clan cats were like ‘wow other group of cats? cool. have fun, we are going back’