What happens if the other side just refuses to close on the agreed date?

A refusal to close on the agreed date, without a legitimate unmet condition or termination right, is generally a breach of the purchase agreement. The non-breaching party typically has a choice of remedies: pursuing a damages claim for the losses caused by the deal not completing as agreed, or, in narrower circumstances, seeking to force the sale through rather than simply accepting compensation instead. Which remedy actually makes sense depends heavily on the specific deal and what would put you back in the position you bargained for.

Practically, the first steps matter a lot. Put the refusing party on formal written notice through your lawyer, document the losses this is causing as they occur, and get advice quickly rather than waiting to see if the situation resolves itself, since delay can affect what you're later expected to have done to limit your own losses. Confirm first whether the refusal is genuinely unjustified or whether the other side is actually relying on an unmet condition or a MAC right of their own before assuming it's a straightforward breach.