Camac,
Whoever gets appointed or elected, as designated by state law, becomes the Senator for that state. So yes a Senator's spouse can replace him/her. I know of no state where that can happen automatically without the Governor, the State Legislature, or the people appointing or electing that person to the office.
Patch,
Yes Sonny Bono’s widow,
Mary Bono Mack, is still serving in the House of Representatives, she was elected to that seat by the people of her district in a special election in 1998 and has won reelection more than a few times since. She is now married to my representative,
Connie Mack IV. He is the son of former US Senator,
Connie Mack III (Connie Mack III was also at one time the representative for my district in the House).
While Connie Mack IV is very conservative congressman and I have no complaints about his voting record, I do believe his marriage to Mary Bono Mack is an example of the basic corruption of the political class in this country. How he and his wife can claim to be residents of their respective districts (on opposite sides of the county) and be married to each other is at best disingenuous and at worst fraud. The only place they live together as husband and wife is in Washington DC. To share a home in any other location would in my opinion immediately disqualify one or both them as representatives from their districts.