Depends if you're running in the black or not, as far as daily bitcoin generation and power usage goes. If you're still coming out ahead, keep it going. If you're not, shut it down.
Selling your rig is a different matter however. If the value of bitcoins goes way up, you may want to fire up the mining rig again in the future and start generating what you can, even if the difficulty rate is significantly higher then. You know the value of the cards will likely go down over the long term, but if the bitcoin price rises enough to make it worth pumping out whatever coins you can at a future higher difficulty rate, then maybe its worth holding on to. Depends on how much you like to speculate.
If you really want out, though, and don't want to deal with mining anymore, sell it all and cut your losses. Maybe keep your best card or two if you game at all, or worry if you get the itch again. Otherwise, 5830s and 5850s are selling for a premium right now, so they'd be great to move.