The Jetstreams were of course around long before BACX/BACON and any of that lot, operating with British Airways Regional. For this reason it is quite possible that BA are the owners of the leases.
If FlyBe do take over the lease they wont be in any position to raise the charges to Eastern, due to the fact that most of the JS41s on the market are currently actively being re-homed. Even if FlyBe withdrew the lease entirely, Eastern would most likely be able to locate a similar number of Jetstreams elsewhere.
At the end of the day I imagine the lease will either remain quietly with BA, or get transferred quietly to FlyBe, with minimum of fuss.