The drive-by media will cover up Nancy's dementia in the same manner that reporters hid FDR's disabilities from the country-at-large during his term.
The seat is hers until she relinquishes it.
Even in the condition that she's in, she can probably win re-election easily enough.
That is, unless another gal comes along like that one in the Bronx, who can unseat her for not being "left enough"...