Is it permissible to sell a plot of land to a Christian, given that there is an issue with the land and he is content with it, and without knowing how he will utilize it, yet with the possibility of him establishing his blasphemous rituals therein?

Selling the land is not permissible if the problem prevents its delivery to the buyer, because the ability to deliver is a condition for the validity of the sale.

As for selling land to a Christian, if you do not know or it is not highly probable that he will use it for disobeying Allah (such as a church or a tavern), then selling it to him is not forbidden. The prohibition only applies if you know or it is highly probable that it will be used for disobedience. His mere worship on the land does not prevent the sale, unless he intends to take it as a place of worship.