"I expect many lawyers will be hired once this Time Stop ends. I want to before that settle non-legal matters; legal ones my Church is competent to negotiate, for the most part." And to Carissa, "if Heaven possesses the means - through Cam or through some other change in the balance of powers - to invade Hell, we would do if we could achieve any of ongoing control of Avernus, denying ongoing control of Avernus to Asmodeus, denying transit through Avernus to the rest of Creation to Asmodeus, or rescuing a sufficient number of people. We would first, of course, tell Asmodeus we were going to do this, and among truly Lawful gods the war would thereby be avoided, as we'd both share our best estimates of how it would go and then agree to skip to the end state. Asmodeus is not, in the framework you instinctively use, such a Lawful god, and would refuse to be legible about whether His estimates were in fact His best, and might spitefully have a war not in His interests. That means that I do pose a threat to everything you care about.
This is a situation that probably will arise eventually, not necessarily with Heaven as a party, because there are a great many entities that object to Asmodeus's rule in Hell and because Asmodeus is not all that interested in avoiding it, if doing so would cost Him his pride or oblige Him to negotiate transparently. Axis is much safer against something like this happening, because Abadar doesn't go around making enemies and if someone had a credible interest in invading Axis He will negotiate reasonably with them for something better so long as something better exists.
Heaven isn't much safer against something like this happening, frankly, but we keep our civilians and our cities on our fourth tier, not the second, because we don't want them to be collateral damage in an assault on Heaven as a military power, and we don't want anyone incentivized to go after them. To the extent there are things precious to you in Dis - and I think there are fewer of them in the real Dis than in the place by that name in your imagination - to the extent that there are, Asmodeus put them there so that some parties that'd otherwise war with Him wouldn't care to, and He doesn't mind if everyone in Dis as a result dies when some party that does want to war with Him does it."