1. Is Kimbreal really the best closer in the league? He's certainly up there, but Kenley Jansen, Aroldis Chapman and Edwin Diaz are, too.
2. How much longer will he be an elite closer? He certainly has not been one since the All Star break.
Re-signing Kimbrel will probably work out in 2019 and maybe 2020. But if he is signed until 2022 or 2023 or later, he absolutely will be a liability at some point. And not a cheap one. Reportedly he will become the mopst expensive closer in MLB history, and if the early rumors are true, by a lot. This will definitely hamper the Sox ability to retain as many of the Killer B's as possible, and if you think it is going to be tough to replace Kimbrel, how tough do you think it will be to replace Betts or Benintendi or Bogaerts? Which of those three would you give up to keep Kimbrel? It is very likely to come down to at least one of them.
In fact, what if it comes down to the non-Boras clients, Betts and Benintendi? Would you rather keep Kimbrel and let one of them walk?
Keeping Kimbrel might help the Sox ability to hold leads, but if they lose the Killer B's, there might be a time when getting those leads to protect is a bigger problem.
This team has found closers before and will again. No need to have the most expensive one because of what he used to be...