Silvio was never living through the coma is what the show intends you to believe.

If you believe Tony dies is the final scene, I think it's about who you feel kills him, or aids in doing so.

I personally subscribe to the theory that Patsy has given Tony up to New York in the end, yet still can see several different possibilities as a viable candidate.

One thing I feel holds true no matter your idea of who may or may not have taken over as boss if Tony was killed, Carlo had become a federal informant and was about to give up anyone in the Soprano faction that realistically would have stepped in to a boss role, Patsy included as he and Carlo shared a book/shy operation. Not to mention everyone but Paulie was directly or indirectly earning off construction which was Carlo's racket.

Given the idea that Paulie never earned legitimate income and lived strictly off the juice of his bookmaking points plus scores on the side, Paulie seemingly would be still named in whatever RICO trial against the Soprano Family was presented by Carlo informing, as Paulie would have likely been implicated in at least one murder minimum given the information Carlo would have known. Same with Silvio, if he was up from the Coma he goes away for the murder of Fat Dom (Carlo implicates Silvo as a direct witness, Muder 1).

So I feel that regardless of the status of his coma Silvio is likely out of the picture of who may be in charge, as is Paulie because they both are almost surely indicted in the RICO case on testimony from Carlo.

I think an unlikely but realistic person to emerge from the hypothetical RICO trial is Benny Fazio, as his star was rising over the final 2-3 seasons but he was never mentioned implicitly in any of the higher earning affairs (mainly construction being an Aprile Crew racket, as Benny came up with Chris) and seemingly handled muscle work until he steadily grew up over the course of the show handling more serious tasks.

This is just food for thought, it's all fan theory.