I really hate the idea of him returning completely, but I would love to see him in flashbacks.

It would ruin the message of the original to have him come back to life or have his death be a fake. I related to this movie SO MUCH because my own older brother died. Unfortunately, we weren't close because he's my half brother and was 14 years older than me. That and him being addicted to drugs. He died two years ago on New Year's Eve. So this movie really helped me through some hard times. It's not among my favorites Disney movies because if has some problems but it's still a great movie! If he is brought back for more than just a flashback than it will just ruin what the original set up and feel more like crappy fanfiction.

Pretty much the only way i'd accept him being in the sequel; bringing him back from the dead is cheap and lazy and it undermines all of Hiro's growth in the first movie,

Or it wouldn't make sense :(

Bringing him back from the dead would be a slap in the face to anyone who's ever lost a loved one.