Technically Scott is "dead", but I see your point.
It can't be the real Wolverine because X-23 is just new taking up his mantle.
I hope it's going to be Jean Grey. if not, then it['s most likely Gwen Stacey.
It's Changeling guys. But he's gonna start using the code name Morph.
Jean is my favorite and I wouldn't say no if this was about her, but I'm fine if it isn't. There are characters you can have duplicates of without them overshadowing everything, but while I can't really articulate why right now I don't think Jean is one of those characters.
As a few folks have already said, Wolverine is an obvious possibility. Goes double when "Death Of" was the Wolverine tale's title.
Could easily be the "idea" some folks have mentioned versus it being a character.
END MISOGYNY NOW, once and for all! Jean Grey 2016.
Like I said, Wolverine only works if you completely ignore development timelines.
Considering he only died about a year ago, that means this would have begun development not long after he died, which defies everything Editorial has said about his resurrection. It's also FAR too close to the debuts of All-New Wolverine and Old Man Logan (which hasn't even release its first issue, yet!).
As for the "Outside" possibilities, I'd guess Namor or Sentry?
The only two mutants who are plausible on this list are Professor X and Namor.
Professor X: Remember Axis and the "visions" Storm has in EXM? Coincidences? We will see.
Namor: Getting wrecked by the Squadron Supreme can't be all that there is to it. Hasn't even the writer himself said that?
"This is me being reasonable"
I doubt it's either Logan or Jean because alternate versions of both characters currently exist and it would seem redundant, especially in Logan's case, lets develop Laura and OML first.
It could be Xavier but I'm going to guess that it isn't going to be an X-Related character.