When Garry Gergich, "Mayor for Life" in Pawnee Indiana, died at the age of 100 in 2048, his wife Gayle looked just as she did when we first met her back in 2012.
I think she may be more like Adam and Dr. Henry Morgan of 'Forever'. She could be killed, but she would come right back to life, naked and in water.
As to why she married Garry and lived in Pawnee? Pawnee was mostly a backwater town where her secret could remain safe. As to spending that eternity with one of the hairiest TV characters since Jack Donaghy, Lou Grant, and Mork.... A doctor in Pawnee finally revealed that secret - Garry had the biggest penis he had ever seen!