Impending Disaster

• WWizards of the Coast2004-10-04
  Official Ruling
  This ability does not trigger at all if there are not seven lands on the battlefield at the beginning of upkeep. It checks this number again when it is going to resolve and does not do anything if the land count is below 7.
• WWizards of the Coast2004-10-04
  Official Ruling
  The ability is not optional.
• WWizards of the Coast2010-06-15
  Official Ruling
  If this card is not on the battlefield at the times its ability resolves, then you can’t sacrifice it. However, you still destroy all lands.

Rulings via Scryfall