I don't know all the details of that. They can be impeached, just like the president. Of course that requires an honest (somewhat nonpartisan) House and Senate, which we don't currently have. As it stands right now, the justice would have to be hated by both sides of the isle, like some of the non controlled justices are. The Dems have no shame and would do all they can to protect justice Roberts. The RINOs wouldn't do anything useful - most would find an excuse to side with the Dems. Out of the rest, I doubt 10% of them have a backbone to speak of. I suspect that in cases of treason, there are other options. A dead judge can't serve on the bench (any more than a dead person can vote). So I guess that depends on who is managing the corpse. In any case, if a judge were to be put to death for treason, impeachment wouldn't matter.