Having spent a considerable time on gardenlaw.co.uk in the past ISTR that if they purposely block the defined access then they cannot just choose another one, the right to use another access is only if the landholder blocks it.
Also that the access has to be for a purpose, the well is long since gone and they cannot dig it up and restore it if it is not on their land so no longer have the reason to use the access and hence it is nullified.
I have a Right of way along the passageway that crosses my neighbours house, defined for any reason so I can do what I want (within reason), but (and this does depend on the wording in the deeds) if I had a right of access to a well to draw water then this would be conditional upon me actually drawing water not just walking to/from it when it's no longer able to supply water.
If it is only "permission" then permission given can be taken away.
They are not allowed to modify the pathway from it's original condition unless it is in such a state that it is dangerous to walk on.
As for adverse possession the squatter has to be in single [exclusive] control of the land, so the owner cannot use it and as they are not and the owner can walk on their own land (and they should) then adverse possession claims would fail.
See here section 2.1
Cutting the grass on a footway is not sufficient evidence of possession.
However, the OP says that they sold the property so the exact nature of this thread is a little puzzling.
If the OP is the landowner of the pathway they can do whatever they want with the land, such as lay gravel or paving, patio, decking etc. especially if there is no longer a need for an access to something that no longer exists.