heh, I would totally enjoy that. Let's put Elena in a tomb under the Mystic Falls Church! Sealed in by a Bennett witch! Damon can wait 150 years for a celestial event to get her out! I think it would be deeply amusing to finish the show with Damon yet again waiting for some woman to find her way out of a tomb. I guess at least this time he'd be sure she wasn't really running around Chicago going to metal concerts, or whatever it was Katherine was doing while Damon thought she was underground.
To be fair, though, they're pretty much going to have to do some equivalent of putting her in suspended animation. After all the build-up to Delena, it would be very hard to move him onto another love interest in the one season they have left, and they have done the 'Damon goes off the rails without Elena' thing a lot, too. A coma would solve both plot problems.