Leareth doesn't see how that could possibly be true of his world. He's looked for hell-like realms although nothing even comparable to this monstrosity and there's nowhere to put them that he hasn't checked. This 'God' would have to be an ontologically different type of being from the gods he knows for it to even be a coherent claim, but if there's even a chance it's true then he needs to completely re-evaluate all of his priorities. He has about a billion questions including what it even means to be earlier in the story of salvation, but the nitty-gritty details can wait.
The one thought he quickly puts aside is that Lev is completely, utterly certain of everything he's saying, and maybe he's right – if there's a 'God' with an ontologically greater set of powers over multiple worlds then maybe this isn't a power that can be defeated by a man, immortal mage or not. Leareth puts this thought aside because five seconds after learning of a problem is far too early to consider giving up.
The confusing part is that, from what he can tell, Lev is...well, he isn't not upset about it, but he isn't, like any sane person should be, blazingly furious that his world is currently in the clutches of an evil god. He seems resigned.
Leareth leans forward, holding eye contact. :Lev, listen to me. Please try not to react too obviously: The worst part is, he expects what he's about to say to be surprising. That Lev may even be angry. Possibly he should take longer to plan his speech, but he's pretty sure that the appropriate response here is immediate, not delayed by the several weeks it would take him to wrap his mind around this.
:This is not the conversation I expected to have: he sends. :I had been planning to ask if your world is in need of a person to conquer the current administration and run things better. However, this is no longer my priority. What I wish to say is – Lev Aarons, you are NOT going to Hell. I cannot promise the same for every human currently alive in this world, because my resources are not infinite and a difficult problem may take a very long time to solve – however, I swear, by every star in the sky, that no matter what happens, I will not allow this to happen to you. I will take you to my world if necessary; I will find a way to make you immortal if I must: It occurs to him that Lev won't necessarily be happy about either of these, but right now, he doesn't care – he needs an ally here, if he's to have any hope of facing the horrifying scope of this problem. :I have fought gods before over much smaller atrocities. A long time ago, I made a vow that I would not cease my work until I had ensured the flourishing of every sentient being, and this vow applies to your world as much as to mine. I will personally ensure the destruction of your shockingly evil 'God', and free the souls already in this Hell, as soon as I can: