yeah Phia has posted a few stories hinting to Helaena's demise. I honestly think Jaehaera will take Maelor's place? Unless Helaena is already super top secret pregnant with Maelor and ends up miscarrying which breaks her. (And to those speculating Aemond will be the father, I highly doubt that).
Jaehaera will fortunately not be taking Maelor's place because grrm confirmed that in his blog post last year.
As for whether Helaena is pregnant or not, we can't be entirely sure. It's just speculation but it would definitely serve them well to have her be secretly pregnant all this time since this will:
1. Justify her refusing to fly Dreamfyre into battle.
2. Feed into her apparent suicide should she lose the pregnancy under stress, which is more close to the book and a better reason than 'destiny demands I kill myself'.
What Phia posted could allude more to the fact that the murder of Jaehaerys and the absence of Jaehaera (who will be sneaked out of KL) has left her feeling empty, and this could as well lead to the deepening of Helaena's depression while she is Rhaenyra's prisoner.
Otherwise, revealing that Helaena is already pregnant with Maelor would be a way to appease grrm and fans a little. They even had Maelor in the opening sequence of season 1, so walking back on the fact that Helaena had him (in utero, at least) was just bizarre and a glaring act of incompetence.
You can also rest assured Maelor (and the twins) is definitely not Aemond's, lmao. At this point it has been disproved by Phia, Olivia, Fabien, Tom and Ewan.