THere is some debate as to whether or not Deadguy is filtered or not and whether there is actually enough yeast in there to harvest. I have had great luck with bombers of shakespear stout, hazelnut stout, and any of the bombers where it actually says pacman yeast on the bottle.
I can't confirm or deny whether one bottle of DG will work, since I usually use multiple bottles when I try to harvest (I leave an inch of beer in the bomber then carefully recapp the bottle with a sanitized cap and store in the fridge until I have a couple three bottles, then add them all at once.)
Since I've never JUST used all DG, I can't tell.
If you look at the similar threads box below, you can see some of the back and forth on whether or not anyone's been successful with JUST dead Guy.
And this is a really great thread on harvesting Pacman....Many of us have done it rather than buy pacman, It was harder to come by only two summers ago, so a bunch of us captured our own....it's fun, and satisfying to do it ourselves.