While I agree that he is dead, I just wanted to make a couple of comments in rebuttal:
-Leia may have just been sensing her son officially cementing his place on the dark side, it is more likely that she, as force sensitive, would feel a shift in the force when her force strong son turns to the dark side (like Yoda and Obiwan felt when Anikan officially tuners and started killing Jedi.) than feeling something for Han.
- Star Wars characters have come back fromMUCH WORSE than a single light saber stab to the abdomen, think Anikan, and even Fin from this episode.
-we don't know how big/hollow this planet is, when Luke falls from cloud city he falls over a mile without a hand and survives. And when Yoda falls from the senate chamber same thing. There may be a gravity anomaly and a conveniently located air ship hangar. There was a lot of time between his fall and Poe's final blows.
Just a couple ways they could explain it if he wasn't actually dead, all can be justified using Star Wars current cannon. Also to ad Harrison Ford himself also confirmed genus in fact dead, and he was part of the decision to do so.