Edit: What's bothering me more is that Serini doesn't seem quite... right. Maybe I'm reading too much into the first panel of this update, but I wonder if she's altogether herself these days. A former hero in long isolation, with some unusual surgery, and whose best friends tend to cling to floors and ceilings...
She's also explicitly stated multiple times she is perfectly fine with however much death and destruction will result from Xykon ruling the world as long as him winning means the paladins and the Order don't have another chance to blow up the last gate. Not quite the most sound logic on display here.
That honestly makes a certain amount of cold sense, looking at the percentages and what she does (and doesn't) know. As far as she's concerned, Xykon is just another garden-variety non-omnicidal evil overlord. No matter how much destruction he does, as long as he doesn't literally annihilate all of creation, he's still better than the Snarl, which she believes will do precisely that. As long as there is life, there is hope: Xykon has no objection to life because he needs something to rule over, but the Snarl is pure, elemental destruction as far as she knows.
Of course, the problems here are manifold:
1. She doesn't know that the gates fail regularly, and that the gods have taken measures to both survive and rebuild the world. Tough luck for any mortals living on the world, but the gods, elementals, and extra-planar entities tend to make it out alive, and if the gods blow up the world early and rebuild, they can even save the mortals' souls.
2. She's got Xykon pegged, but she doesn't know about the ambitions of Redcloak and the Dark One. If you want something that will panic the gods, the belated realization that someone just cast a spell that put a god-destroying, reality-destroying creature under the control of someone who both mistrusts and is mistrusted by the gods would rank highly. Xykon and Redcloak getting anywhere near the gate would not only all but guarantee the destruction of the world once they fire off their spell, but also lead to the possibility of a god-killer actually getting loose and killing one or more of said pantheons in the collateral fire, or worse, all of them, if someone among the gods decides to either call the Dark One's bluff or go for a preemptive strike out of fear that the Dark One will release the Snarl anyways just to thin out the competition. Or, for that matter, that the Dark One might actually release the Snarl anyways in the hopes he can control it; we have very little feel for the Dark One's personality or what he might or might not actually do if handed the reins to a god-destroying creature, just his stated intentions.
3. Even with what she does know, she hasn't thought through the consequences of evil overlords who have a single massive power source that comes with a handy self-destruct. This may be because her party didn't have a bard, but anyone familiar with narrative causality knows that nothing gets heroes crawling out of the woodwork like evil overlords blatantly throwing their weight around, and said massive power source is inevitably going to be destroyed by a hero just in time to unleash the Snarl for the season cliffhanger.