Can I just not choose an Ascendancy?

Maybe a bit of an odd question, but, I tend to suffer from choice paralysis.

Background:
I managed to get through the first trial of Sekhemas with my level 30 mercenary.
First try and all, my character has low damage and poor equipment, so I'm already used to constant kiting and dodge rolling, though that honour mechanic still sucked.
But now I am supposed to choose between two ascendancies, and to top it off I apparently can not change them later (not that I ever did that in PoE1), and I'm absolutely not prepared for that. I haven't even beaten act 2, I have no idea what would feel good later in the game. I haven't even decided on a main skill yet.
My first impression is that I don't really care for either of them.

Question:
Can I just walk out and then do another run later to choose then?
Or will it then randomly choose one for me?
I really don't want to risk the latter, so I'll stay in that place and leave the game running over night.
Of course, this is assuming I can even try again with a level 22 run, I doubt I'd survive one anywhere close to my char level.
So, uhh,
Question 2: Can I?

Being unable to change your ascendency is a facet of the game being incomplete. It will get implemented eventually.

It is my information so far that it might, not that it will.
Still, I'm just not ready to decide yet.

It took me probably some 15 hours to get to this point, so just restarting isn't an option. I'll think about it a few more hours.

I mean, I don't know why you would pick a class that you didn't at least check out the ascendancies on beforehand knowing how PoE is. If it makes you feel any better both are very good.

I didn't check anything beforehand, not the passive tree, not ascendancies.
I wanted to go into this and just enjoy it for once.
Granted, inbetween I spent several hours just musing over where to place my next skillpoint, but that probably illustrates the problem.

So far I started wanting to go for rapid shots, then found that ability too likely to get me killed, so I switched to armourbreaking gas grenades and fragmentation shot. Who knows what I'll be using in 5 levels.
And just like how in poe 1 I once carried the sekhema's feather around for 10 hours because I didn't want to decide who to give it to (utterly inconsequential for the player), I'm not quite willing to decide now.
I did look it up now, and it turns out for poison I'll have to go with ranger instead (pity how there seems to be actually less freedom in off-classing in part 2, but it'll come with time), but that still doesn't inform me on what I'll be doing going forward. I'm not ready to decide until I've tried at least every single crossbow skill, and that's probably another 15 hours down the road.

Edit: The way I see it, the game tries to force me to roll the dice on how it will take agency away from me in the future.

So it comes down to this:
If I just leave that room, will I be able to later get another balaba's bayra and go there again?