Considering what the gods can and cannot do, let’s near in mind that the Norse gods or the Finnish ones aren’t supposed to be almighty. The Norse gods battle with the giants all the time (except when they are fighting amongst themselves) and aren’t by any means always victorious. So the fact that they haven’t saved the entire humanity does not necessarily mean they aren’t around at all.
I know they aren’t omnipotent, sorry if I made it sound like I believed that when I started talking about them (I might have exaggerated by saying they would “rid the world of the illness once and for all”). I meant to say that, by now, 90 years into the future, if they would have came to Earth at some point during the century, they would have made significantly more progress in expanding the Known World, even if they sometimes lost some battles in the process and had to retreat and regroup. Omnipotence wouldn’t be required of them to at least show up and help with the cleanup, while at the same time granting powers to the ones that seem worthy of them, like they do in the comic. If they didn’t have anything to worry about regarding the rash and the well-being of their own world, then coming to Earth should have been their first course of action.
But again, if they were also affected by the rash then that would explain the unwillingness of the few that survived to stay in the physical world, since it wouldn’t be any better than just staying in Tuonela (going with the theory that it’s a refuge for the surviving deities). Wether they stayed there or came to Earth, they would still only be able to bless humans, since, if they ever were to start a crusade to reclaim the “Silent Lands” they would most likely die and then there would be no one left to continue gifting powers.
Also, on the topic of omnipotence, I think we have to assume that there are no omnipotent gods in the ssss universe, as that would pretty much make the story unnecessary. Let’s take for example the Catholic God. If he were omnipotent then the rash wouldn’t have happened at all, erased Thanos-style with a snap of his fingers. Also, if he were somehow corrupted by the rash (going with the idea that the rash is literally out of this world, hence out of his control) he would have became as hellbent on killing all the still living humans as all the other trolls on Earth and, with a simple though, destroy everything. And this would go the same with all the presumed to be omnipotent gods of the real world.
And thorny’s insight is very important! It could well be that the way Iceland was saved by the gods could be divine intervention to make them close borders at the time. Remember they didn’t leave any time for their citizens abroad to return so they must have been extremely determined. There is a thriving and officially recognized religious community of the worshippers of the Norse gods in Iceland in the present day real world, so it could be plausible to think there was a communication channel open.
I suppose that might also be true, though I don’t see what sacrifices the Icelanders believe the gods had to make in order for them to survive (adv 1 page 67), other than wasting a few minutes to tell them “Hey, you better close your borders or you’ll end up über fkd”, if they objectively know (not just believe) that the gods helped them.
But, even if this were true, it wouldn’t mean that they survived following that short exchange of words. I think them warning Iceland would actually be in favor of the theory that they were also affected by the rash. Because, if the gods warned them before even the first patients started trollifing, then they must have known what the plague was capable of doing. And, since they’re not omniscient, wouldn’t seeing it affect their own people (before spilling over into the physical world) be the only way they could have known about the danger?