Two sides, and both have to survive
A covenant has a burden — the obligation on the land that is restricted — and a benefit — the right of the land that was meant to be protected. For a covenant to be enforceable today, both have to have passed down to the present owners of the two pieces of land.
The rules differ depending on whether the covenant is negative (do not do something) or positive (do something), and they differ at common law and in equity. Positive covenants in particular do not readily bind successors, which is why developers go to the trouble of deeds of covenant and title restrictions.
The practical consequence is that a covenant's existence on a title is not the same as its enforceability.