This is a sticky topic. The rights of a purchaser in a sales contract do not simply disappear. They can cloud title unless released.
A title insurer will consider the length of time that has passed since the date of the contract and the circumstances before deciding whether or not to insure over the equitable rights of an unreleased purchaser.
The issue is most often a seller holding hand money. If the seller hasn't come to terms with a purchaser and obtained a full release of the contract, technically the purchaser may still have the right to complete the purchase. Be careful and if necessary seek legal counsel.