Not sure if this is intended, but... (spoilers)

Nahkriinaak

I can't quicksave during the final fight in hell. Usually if I just get out of the line of sight of any enemy it lets me quicksave, this has been extremely useful because I always seem to lose my saving throws against spells no matter how high they are, so I can just spam Q and L and keep trying until my luck stops being terrible. This is especially egregious because Irenicus can cast spells in slayer form (and not take damage from being in the form might I add) while I cannot. It also does not help that I likely built my party very very badly due to my incompetence.
Is there some way to force a save outside of vision of Irenicus? I'm on my 8th attempt (4 of those due to dying from disintegrate) and I'm gonna go nuts soon.

abacus

Yeah, I'm pretty sure it's intended. Once he shows up, you have to take him down them and there... If you think that's rough, wait until the end of ToB. There really is no rest for the wicked.

xzar_monty

The game works as intended here. At that point, you're supposed to be able to make pretty solid tactical judgments. The fight is not really that difficult.

There are ways to improve your saving throws, for example. It's a good idea to keep a nice stack of potions that do that...

Fardragon

You might try killing the demons then hiding from slayernicus until his spells wear off.