Ginsburg is around 84 years old and Sotomayor has Type I Diabetes and is about at the end of her expected lifetime with that disease. Breyer is old too.
John Paul Stevens served till he was 90, and he’s still alive and kicking after 8 years of retirement. Oliver Wendell Holmes also served till he was 90 and lived four more years after he retired. Ginsburg, Sotomayor, and Breyer will die on the bench, and that could be 6 or more years away.