In the last forty years:
93 incumbent Senators were defeated for re-election (not counting the two defeated this year, since we don’t know their futures yet).
9 of those ran for Senate again
6 lost on election day
1 polled so badly that he dropped out before the election
1 of these winners was kicked out by the voters again later in his Senate career.
The other originally lost his Senate seat in a primary, so his circumstances may not be applicable.
4 ran for Governor
Let’s assume for the sake of argument that Brown is definitely part of that diehard 14% who didn’t give up. His odds of recapturing the Senate seat are about 22%. Not nothing, but I wouldn’t call him the favorite. And since there would be a high probability of getting the boot again later even if he won, it’s probably not worth it for him to even try.
His odds at a Gubernatorial seat are 50%.
The takeaway from all of this: You really only get one chance to impress the voters as a Senator. When they say goodbye, they mean it.
If Brown is rational, he’ll go for Governor in 2014, or become a lobbyist and give up on elected office.. The Governor’s race is what we should be afraid of. In the meantime, President Obama should appoint who he wants to his Cabinet. If he genuinely prefers Rice, by all means appoint her. But if Scott Brown is the only thing stopping him from appointing John Kerry, he should appoint Kerry.