Actually at her age it is an entirely realistic possibility, just mentioning that (In effect) a range of causes from retirement to mortality might stop her from returning is really not all that outrageous.
Even Congresscritters die, it just seems to take them a Godawful abnormally long time to do it. But since she is a Dem from moonbatland, I'm not sure even death would necessarily prevent her re-election, and I'm positive she'd still vote in the general election.