Are we to understand that this lady gave the land to the parish? And when the land was conveyed, the deed of conveyance included an express term stating that the land was to be held in perpetuity for the benefit of villagers and their children? So the beneficiaries are both identifiable and existing? What are the precise terms of this covenant?
This seems, in effect, to be a trust set up, with the Parish, in the form of the Parish Council for the time being, as the trustees and the beneficiaries the persons identified in the deed. On that basis, any beneficiary has the right to stop the Parish from breaching the terms of the trust created. So long as there is a beneficiary extant , that deed remains valid. Only if there were no villagers would it fail.
It would be a very curious consequence if the Parish could either sell the land without that covenant passing with the land, as covenants generally do, and binding the new owner or decide to change the nature of the land held by revoking the term. Bear in mind that Parish councils commonly have land in the parish declared 'amenity land', whoever owns it, a declaration which results in the land being kept as it is and not developed, because it is regarded as of benefit to the parish. With that principle established, it would be odd if a parish could deliberately remove land from the benefit to the parish when it had been established for that very purpose.
But wait to see what Barmaid and the rest of the lawyers on this site think. That's my take on it. There is perhaps a charitable side to this deed, but I don't see that that is relevant.