Brits are going to face some default financial hurdles before it gets better with Brexit. US is absurdly deeply in debt, I doubt tossing them a few billion US dollars is going to be that difficult.
England could continue having fishing rights, and the original natives can lobby the US directly for resettlement (unlikely to ever happen in either case.)
Would mean the UK would be flushed with a internationally accepted currency at a crucial time. Brits don’t have much use for the location… If they got it back, doubt they could make nearly the use of it we can.
So, should the US just buy Diego Garcia, sell some funny money dollars for it before our own currency goes down the drain? We would still own it afterwards.