I had the same concerns, and for a while we did have to stick the dummy back in once or twice each night. But we were still in the same room and, frankly, if it's a choice between sitting up and putting a dummy in then everyone straight back to sleep, or no dummy, shushing, patting, rocking etc then I'd go with the dummy every time. DS learnt to find it in the night and put it back in from about 8mo.
Like a couple of people have said, we just use dummies for sleep, and sometimes in the car. It's a good way to indicate what's coming next.
Oh, and a cranial osteopath said to a friend of mine that it's preferable to suck a dummy than a thumb, plus you're in control of it. You don't see many 8 year olds with a dummy, but plenty still suck their thumbs well beyond childhood!
I'll definitely use one again with my next baby.