Does Snowe's retirement make her more or less likely to retire? On the one hand she's lost her colleague and friend, on the other hand she was always kind of overshadowed by her "twin". It might depend on how she gets on with her new moderate hero colleague, King (despite him caucusing with the other party).
The relationship between Collins and Snowe was always tense. While Snowe grew tired of the Senate in late years due to the partisanship, Collins enjoyed her newfound power as a moderate Republican. In fact, I think Snowe's retirement and her corresponding rise in seniority/profile makes her more likely to run (not that she was going to retire in the first place).
This. I don't see her retiring. She's become too powerful to primary.