Death penalty for treason would be a fitting end to Musk's story, I think. It doesn't look like anyone has gotten a death sentence under federal treason laws since the Civil War, though.

The terms used in the definition derive from English legal tradition, specifically the Treason Act 1351. Levying war means the assembly of armed people to overthrow the government or to resist its laws. Enemies are subjects of a foreign government that is in open hostility with the United States.[6] Treason does not distinguish between participants and accessories; all persons who rebel or intentionally give aid to hostilities are subject to the same charge.
source

Russia might not meet the bar for "open hostility", I'm not sure how that is defined. This layman sure as hell thinks Trump and the January 6 mob fall into the definition of 'levying war' though. And interestingly a conviction of treason also forfeits your right to hold public office, even if your punishment is prison instead of death