Well, his track record in Detroit for signing expiring contracts was not really that good. That team is still stuck with Miguel Cabrera for 5 more years at $154million, and Cabrera is already closer to needing a wheel chair than he is to making an All Star team.
We get the point that another pitcher isn't going to simply step in and pitch like Kimbrel did. Kimbrel himself might not even be able to. And, as fans, we have the luxury of loking at it one yaer at a time and solely focusing on talent. But Dombrowski doesn't have that luxury. And if Kimbrel's contract starts approaching the early speculation - which is not unreasonable - it should be a difficult decision to being him back, because there will be ramifications on future moves.
And really, as Slasher pointyed out - how necessary is Kimbrel? The Sox have won 107 games and are 10 up on second place. Where would they be without Kimbrel? Maybe 7 games up? He isn't the difference in the division here.
Betts, on the other hand, might be. He is a guy the Sox need to start focusing on ASAP, assuming he (and his agent) is willing. And it certainly is possible that DD has already put that in motion...