I doubt the SCOTUS will strike it down. There are several crimes in state and federal codes that allow the death penalty (i.e. rape and kidnapping). The SCOTUS is more interested in how the rights of the accused are handled. In my opinion, it will be more likely that we would see a case where the SCOTUS strikes down a specific class of defendants (like juveniles or the mentally retarded) that to strike a specific set of crimes. If the SCOTUS killed the death penalty for sex crimes, how far would it be to strike it down for treason? The Constitution does not explicitly say which crimes can be punished with death, and I think that with our new justices, it will be interpreted that way. State Supreme Courts are another matter.
It's not a question of striking it down so much as it is a question of overruling their previous decision in Coker v. Georgia, which basically struck down the death penalty for anything other than murder. It doesn't look like there are five votes on the Court to do that.