Tiamat after Endwalker. Spoilers for EW and HW

I'm finally doing the questline to get the Haurchefant emote where you go around to various places, essentially reliving the story. Well there's a part where you go see Tiamat, and after Endwalker Tiamat isn't there. Clicking on the location node still plays a cutscene with Tiamat in it, but I figured these kinds of things happen, no big deal. Except the last line of the cutscene is "..Perhaps there was hope for them. Perhaps, this time, they would learn and remember. But her part in the tale had ended long ago. Within this monument to hubris would she remain until the end of days...beyond redemption..."
And then I came out of the cutscene and Tiamat was gone. I don't know if it's worth it for the devs to make an alternate thing for post EW players, but I thought it was worth mentioning at least.

I'm not exactly sure what you're asking for, but all side quests are in their own time bubble. It's why you can complete EW but then go do the Drg quests where you meet Estinien for the first time. Or back during 2.55 people could go and do the lv 50 Cul quest and have a Nanamo who wasn't dead as that's what people thought back then. The game for the most part figures you'll have gone and done all the non MSQ stuff at some point. This included the Crystal Tower until 5.3 and the Devs felt it was too important to allow people to not have done it before reaching the Trial in 5.3.