Firstly if you haven't watched PB: The Final Break then I wouldn't read on cos it may spoil it for you.
Prison Break: The Final Break kinda redeemed PB (a little) after what was a poor effort at the end of Season 4.
Regarding Michael and whether he's dead or not, knowing PB they could easily bring him back if they wanted to make a future Season. They bought back Kellerman and would Michaels return from 'the grave' be more unbelievable than Sarah's return?.
Remember if you havent seen the body then there's no proof they're dead and Michael's death wasn't reported.
That video message to Linc and Sarah could have been genuine at the time (before Linc and Sarah found out he was alive) and as for the grave visit at the end of S4, well that could have been a 'show' for the feds who were watching.
Don't get me wrong, I do actually think Michael is dead and that the TV people are done with Prison Break but if they did want to do another season they could....
and with Michael in it.