At the end of the day it really depends on the financial situation of his family. Drummond already established the fact that he's not a normal kid when he gave up his scholarship for Mike Bradley. That was a great gesture on his part by all means, but in addition to Drummond being a great kid, I think it shows that he's either in a financially stable situation and/or money isn't as important to him as other things.
I do think the "injury" risk is a bit overexaggerated, though. Even if he blows out his knee, there is a good chance he's back within a year and retains 99% of the athleticism he wants had, considering the advancments in medicine and technology. Barring any sort of dramatic event, the kids infiinite ceiling and potential won't go anywhere over the next year, regardless of how quickly he develops. Even in the case of Greg Oden, he probably could have sat his sophmore year at OSU, put together a couple of good workouts, and still been picked in the top five. Point is, the money is always going to be there for Drummond. Even if he doesn't show any improvements over the next year, he's still a lottery pick based on his Godly physical abilities.
I would advice him to stay another year, but it's a very difficult decision and I'm sure us boneyarders will support him either way.