Firstly, it's a staple of mortals in general to die.
I should correct myself then. "All heroes die in brutal ways, defending what they believe in. The term "Hero" tends to not be truly decided on until said person is deceased and the look back on how their life was carried out was done. Not by wide opinion anyway.
Let us have a game of logic shall we? Logic would--after all--indicate that a good amount of people would think Rock was just as bad as Wily's bots simply for being in the fray after all. People caught in the crossfires of Wily's robots would see Rock and a good enough number would think "Damn robot! Always the robots!" like little bigoted people they could be.
For that sake, at the present time of his actions, he could not be deemed a hero.
Only until after him dying and they would look back on what he's done for them, and now, their left open for any attack without anyone there to defend them would he truly be deemed a hero for what he's done. Under that logic, only after his death can he be considered a hero. Until then, he's a robotic crime fighter.
But that would never be shown in the -Classic- game series. So that kinda makes my point a moot point, now doesn't it? >_>
Secondly, Rock being a robot would get repaired, like anybody else in the series.
The X Hunters and King would like to have a word with you.
Third, time travel and space are all possibilities for Rock to get out of the setting without having to die for the X-series to occur.
I highly doubt Rock went to the future or past to live a new life away from everything he's defended. Maybe ---MAYBE he could have left the planet with Duo but at best, that's fanon guess's. And it's not so much that his death would be vital to the X-series occurring but rather, would give X more meaning. To have a name to live up to, one to honor and one to deserve and carry after the original Rockman would be deceased.
Rock's death would carry more significance to X and that series than "Rock went to become a robot with Justice Energy like Duo", or just becoming Quint and that's it.
While I don't believe that Zero killed him and everyone else, I do think he went down swinging.