Hit a completely unmarked rock far out from shore. The prop is bent up and the boat will not go into drive, only reverse. It is a bravo one drive. Will I need to now replace the lower unit, or the the complete unit? What a disaster.

It could be one or more of many things.

You really will not know until you get into it and see what is there (or not).

Depending on the r's you were turning; you might have extinguished the entire drive or simply knocked it out of adjustment.

While a drive might be considered a weak link my experience has also proven there are times when they are shocking with what they can withstand.

The fact it will go into reverse and not drive, in-and-of itself, really doesn't mean that much.

Granted, the likelihood of a minimum of some severe damage is good; from what is currently known, it can not be judged until the parts are spread across the work bench!

Call your insurance company

I can only assume that there is a noticeable flat spot on the nose of the lower from the rock - if so, the shifter spool right on back is/could be messed up.... the two previous responses are right on the money - tear down to see exactly what you have and call the insurance co.

make sure you have under water coverage for the boat..