Don't know if any of the Lib USSC Justices are in ill health. OTOH, Justice Thomas is getting on in years and might decide to retire when Trump is in the WH. I'm pretty sure some of the attacks by Dems on Thomas were in hopes of Kackle-a being the President to replace him.
WRT J. D. Vance, my suspicion, when I saw he is relatively young, was that Trump picked him to boost his visibility for 2028 and beyond. If my suspicion is correct, look for Trump to tap Vance for something significant and visible ... maybe even "Border Czar",

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