Well, we do know under certain conditions $365 million could retain him. Whether or not being out of Boston was one of those conditions is another matter.
But if we go extremely hypothetical (based on my old commentary about transactions in the 2015-2016 offseason), and we revisit the Price/Kimbrel acquisitons.
Dombrowski traded for Kimbrel and signed Price. History has shown it is cheaper to sign a closer (as they rarely demand 7 year deals) and trade for a starter. Had the Sox signed a closer that offseason and traded for a starter, would they have been off? Price was a good pitcher, but was only worth 10.6 fWAR for the Red sox from 2016-2019. Similar pitchers (whose availablity I cannot guarantee) include Chris Archer, Lance Lynn, Gio Gonzalez, and Tanner Roark. If the Sox had dealt for one of them and signed an available closer that off-season and received similar production, resetting the tax limit without Price ($31mill AAV) and without my oft-questioned extension of Eovaldi ($17mill AAV) might have made it possible to reset the tax limit after 2019. Now, if that had happened, and yeah, there can be no certainty here, but do you think it might have been possible to retain Betts?
Henry's generosity does seem to be rather mercurial, and it appears that he really changes his habits based on spending the Luxury Tax payments that have no ROI.
I know. A more hypothetical post is hard to see here. But it seems like too many moves were made without ever considering that Betts would be the unaffordable one. And I have not even delved into the Sale extension, which is looking more and more like Sale jumped at it knowing his own health situation. Why else would the poster boy for Underpaid Contract Extensions leap at a second one?