Let's see, (major) faction by faction:
Imperium is still the biggest on the block, but with the galaxy covered in Warp storms it can't fight as a whole. On the other hand, with Guilliman's legendary logistical ability in play... if Mars manages to get the Imperium back in the tech game, there's absolutely no reason humanity can't go into a fairly convincing second Great Crusade. The problem is that it's fighting nearly EVERYONE, with only (part of) the Eldar as nominal allies. The situation is ridiculously grim, but there's hope and that's more than it has had for millennia.
The Eldar too have hope, but they sacrificed a LOT for it. Commorragh is effectively gone, their most powerful military craftworld, Biel-Tan, is in tatters, and their population issues aren't going anywhere. For all that it was used for irony, Vect's "What fool would plan to defeat their enemy by dying forever themselves" has some definite truth in it.
The Orks... meh, they've already won. They've GOT their victory condition.
Necrons will probably accelerate waking up where they can as Chaos breaking loose... probably not in their best interest. If the Silent King gets things together they'll still be focused on the Tyranids. TBH, it's hard to see if any of Gathering Storm will even have any effect on their actions beyond slightly annoying some of their Lords.
The Tau... are actually screwed. Oh, they'll probably pull through by weeabo author fiat, but last we saw of them they were all about to become Tyranid snacks and had lost Aun'Va (and the world he was on) to an Imperial counterattack. Shadowsun needs to step the hell up to the plate, and preferably make friends with Farsight. I don't think they can count on the Imperium to bail them out of THIS Tyranid attack... It's a bad day when you need to pray you accidentally colonized a Necron tomb world, but it might actually be their best hope.
The Tyranids... Much like the Necrons, unlikely to be affected by recent events, but from what we've seen of their interaction with Chaos, they might well end up biting Abaddon in the but (bonus points for doing it literally).
As far as we know, Chaos is currently the only one that currently DOESN'T have something horrible happen to it.
Ask not the Eldar a question, for they will give you three answers; all of which are true and horrifying to know.