Eh, dead or alive does not matter. Shepard's story truly is over, IMO.
Kinda reminds me of this one episode of The Twilight Zone I once watched. In it, this guy aspires to be the greatest pool (or billiards?) player ever. So, he goes to heaven iirc and faces the last guy considered the greatest ever ("Fats"). They agree to a game, and all along the way, Fats ridicules the main-guy -- all the way up 'til main-guy wins the match over him. Fats, however, is relieved to be defeated and leaves. And now, main-guy holds the mantle of being best pool/billiards player ever.
Then he realizes why Fats ridiculed him and was glad to lose -- as the best-ever player, he had nowhere to go anymore. So he was stuck, up there, doing nothing but defending his title, hoping the next guy would claim the crown from him. It's kinda the same deal for Shepard. He has, in some fashion, conquered the Reaper threat. Now what?
It's also like that moment with Zaeed in Citadel DLC. After he finally wins, he wonders what to do next. "More claw?" he muses. Shepard can dissuade him from playing it again, though, telling Zaeed that he is not going to top that victory and that now really is the best time to walk away (Citadel DLC had lots of underlying messages).
In my headcanon, I hit on a way for Shepard to return in Synthesis, but I ultimately abandoned that development because I had nowhere to take his story.