well judging by the flow of FT grey is either not dead or will be brought back to life/will make his death mute through timetravel
I was really surprised when it happened, I know ppl wanted something like this but I really want Grey to be back (which I think is gonna happen ofc, but still

), at least the way he ''died'' was awesome (I really don't know which word to use), It was totally unexpected on my part ... Hey Juvia I have something to tell you ... I was thinking: ok here come the funnys ... and than BAM
theres still the possibility of an ice clone, but I don't remeber did his previous ice clones blead? didnt they just immediately turn to ice?
theres also ultears time magic or some other magic possibly
anyway maybe a lot of main chracters are gonna die and than time travel is gonna change that, but that from what we have seen until now would mean that (if Grey and any others really die) the ones we know and have followed since ch. 1 will STILL be dead because as we have seen timetravel in FT most likely creates another reality so the ones actually saved by time travel would be another Grey etc.
as far as I know Hiro isn't a physicist or anything like that so I hope he is very careful if he goes into timetravel and dimensions ...