In the United States and Canada, burial plot leases generally don't expire in the same way they might in some other countries, where land constraints or laws lead to temporary plot use. In most cases in North America, burial plots are sold as perpetual (permanent) interment rights. Once purchased, the plot is generally intended to be used for burial forever, without any expiration or requirement to move the remains.

However, there are a few specific scenarios where remains might be moved or plots reused, though they are rare:

1. Family Decisions: In some cases, families might decide to relocate a loved one’s remains to another location or family plot. This process is known as disinterment and requires legal permissions.

2. Cemetery Abandonment or Land Reclamation: If a cemetery falls into disuse, or if a municipality decides to repurpose the land, legal procedures are typically followed to handle the remains. This situation is very uncommon, and usually, if the land is reclaimed, remains are respectfully relocated to another cemetery.

3. Columbariums or Cremation Niches: Some niches for cremated remains in columbariums are leased for a specific period. When the lease expires, families may have the option to renew or relocate the remains.

Overall, perpetual care is the standard in the U.S. and Canada, making it unlikely that graves are moved or reused unless absolutely necessary.