If we assume 10 as the max. The have at least 40-50 flights left in the boosters the have. Now some of those a reserved for NASA/DoD and while they can be reused, they will likely only be reused for those costumers. So in practice its a bit less.

If they can go significantly beyond 10, say 20, they have years of booster left if they want to.

I think they might only need to produce like 5ish or so more and that should mostly be fine until Starship destroys the market for the F9.