I used to worry about eels dying and rotting, but then somewhere on MFK I read a story about a 2 something (2 day, 2 week, 2 month, 2 year, I cant remember at all..) earthworm COMPLETELY ALIVE every time they vacuumed the gravel (so probably at least a month)
So now I just throw worms in whatever tank I feel like and forget.
And I have found some truth to this.
Usually if the worm is being attacked by fish it will die..
But there are some worms in the various tanks here that live at least a few days.