Is it permissible for the questioner to reclaim or purchase land that his grandfather endowed as a waqf, and the Endowments Administration has since declared it no longer needed and offered it for sale?

It is not permissible to dissolve an endowment (waqf) or dispose of it as long as its benefits remain, based on the Prophet's (peace be upon him) statement to Umar (may Allah be pleased with him): "If you wish, you may dedicate its essence [as an endowment] and donate its fruits." The majority of scholars hold that it is absolutely impermissible to sell an endowment. Imam Ahmad, however, believes that it is permissible to sell and replace it if its benefits become completely lost or if there is a compelling public interest (maslahah) for doing so. Accordingly, the aforementioned land must remain endowed as long as it is possible to benefit from it, and the heirs are not permitted to reclaim it. However, if its benefits become lost and it is in the public interest to sell it, then there is no objection to selling it at that point, and you may purchase it.