Alita: Battle Angel and The Expanse share the same universe, with Alita being set a few more hundred years in the future.
A sequel, if it gets made, will hugely compress the events of the original manga, and rush to The Last Order
The way Alita is openly antagonistic against Zalem in this continuity makes it very unlikely that she'll ever work for them, so it's unlikely her adventures in the wasteland will be adapted. Furthermore, the movie placing Nova in
Zalem, as their leader, seems to point the future in that direction. Nova may even get merged with Mbadi's character, with Zalem standing in for LADDER as a whole.
- Jossed by Word of God - the next film is going to cover the Motorball arc up to Alita vs. Jashugan, if it gets made.
- Motorball arc precedes the TUNED arc, so it's still not completely out of question yet.
Flashback Nova and current Nova are not the same person.
Current Nova is actually a clone or a distant descendant.
- While Manga!Nova is younger than the Film!Nova (he basically just looks like his real age), one of the most direct and immediate results of his research was him indeed becoming functionally immortal, as in almost impossible to kill, and he revives then anyway. So this assumption is simply not necessary. In the manga setting, the indefinite life was known in the Earth Sphere even before the war, Nova just added the revival twist.
If there is a sequel Chiren will still appear.
Her heart and especially her brain appear to be in some sort of life-support system. Ido has already demonstrated the ability to rebuild entire bodies. Alita knows where her brain is stored and Vector never had the chance to send it up to Nova before being killed. Provided you can hook all the casing up properly, no reason she couldn't be revived as a full-conversion cyborg.