The second law of thermodynamics indicates that if you leave the drive sitting and do absolutely nothing with it, the signal on the platter will eventually degrade as the magnetic forces fade toward equilibrium. That process takes an unknown amount of time, but experience suggests that the longevity of the data tends to outlast its relevance.
That said, non-passive environmental factors such as heat and vibration can have a devastating effect on data recoverability, particularly in the drive's current state where something may already be physically wrong with the drive, the situation tends to deteriorate more quickly. And more importantly, the data will not become easier to recover on its own than it is right now.
If the data is important enough to warrant the cost, then I would recommend sending the drive to a center where they can work around broken components to recover the data.