Oh, sure. They COULD come back at any time. I'm not sure they'd want to, given what they'd be coming down to. They'd have better luck hoping a carrier group was available and rash-free.
That's a thought. What kind of communications equipment do they have on the ISS? Would they only be able to communicate with specialized places designed specifically for that? Or once they're back down to Earth, would they have an emergency signal or something? And if so, I wonder what the range would be.
If they can only communicate with places that have special equipment, which seems most likely to me, then they might not have a clear idea what exactly is going on. They might catch that there's some kind of pandemic, but by the time people are turning into trolls, I doubt there would be anyone to communicate that to them. Given that, it might not be too much of a stretch to imagine that they'd assume that something really, really bad happened once things went quiet. I think it is a bit more of a stretch, though, to jump from there to the conclusion that the whole world is dead and they should try to come down near an isolated island where people might have survived. I think it's more likely that they'd try to come down near a major nation.
As far as carriers go, if they come down very soon, any major nation would do--a lot of nations have them now. Any later, though, and a lot of those carriers will run out of fuel and be unavailable, in which case they'd have to come down near the US or France, since those are the only two nations with nuclear powered carriers. Many more nations do use nuclear submarines, though, so there could be hope there, too. They wouldn't be as well equipped for picking up survivors, but the ISS doesn't really have enough crew to make any appreciable difference. I'm sure they would be able to manage. So, provided they have some kind of emergency signal that carriers and subs are able to respond to (which seems likely to me), the candidates are: the US, France, England, Russia, China, and India.
This is all if they wait until after the disaster fully pans out--it's definitely possible that, right before things went dark, somebody told them that they should really return as soon as possible. In that case, some kind of pickup for them could probably still be arranged.