SC justices are appointed by the president and confirmed by the senate. Both are currently held by the democrats, the latter narrowly. Both are likely to flip next year. Sotomayor is over 70, diabetic, and travels with a medic.
If she wanted to do the right thing for the causes she believes in, she should have resigned during the past one or two years. Biden would have been able to replace her with a younger, equally liberal justice. But she didn't and probably won't, so if she dies anytime in the next 4 years (or 8 years if the Rs win the presidential election after that) then the court goes 7-2 and will remain conservative-dominated for decades.