They may not sell a synagogue except under the condition that, if they wish, they may repurchase it —- this is the opinion of R’ Meir. The Sages say, however, they may sell it permanently [and for any purpose] except for [the following] four uses: as a bathhouse, a tannery, a mikveh, or a water closet. R’ Yehudah says: They may sell it as a courtyard and the purchaser may do as he pleases.

R’ Yehudah said further: In a synagogue that has been destroyed one may not offer eulogies therein, twist ropes therein, spread nets therein, spread produce on its roof, nor use it as a shortcut —- for the Torah states, And I shall make desolate your sanctuaries; [this implies that] they are holy even when they are desolate.  If grass grew [in the ruins], one may not detach it, because of grief.