This is a question that had me thinking hard a few years ago.
My Sherman is pretty rare as Shermans go being one of only a handfull of M4A4s in running condition with the correct engine and one of only three 'standard' 75mm gun tanks of the type.
My Cromwell is even rarer, a genuine 1RTR Normandy veteran, though still to be restored.
When I aquired them, prices were nowhere near what they are now and I seriously considered leaving them in my will to an organisation rather then them being sold off to the highest bidder and disappearing abroard.
Bovington do not have a standard Sherman 75mm gun tank as used in large numbers by the British Army neither do they have an exhibit with a British NW Europe combat history.
The thing is, now that The Tank Museum have to cater to the masses for their survival, I'm sure the sherman in particular would be used for the mobility displays until it broke and would then be shoved in the back of the reserve collection building. This is in no way a critisism of The Tank Museum, just an observation.
However, now I have a daughter and with WW2 tanks making good(!) money, they would have to be sold and if that is a result of my demise, I can't be worrying about where they go or what happens to them!
In the meantime, I have no intention of selling them and continue to enjoy them to the full.