Rehab, rehab, rehab. Range of motion and strength. I've had 5 surgeries on my right knee and it's basically waiting to be replaced once I turn 50. Muscle atrophy is a huge issue so even if your just doing flex exercises in place, keep the muscle doing something. If you were in good shape before the injury, it will be faster. If your in your 20's and athletic if will be faster than 40's and not so much. If you weren't in good shape, losing weight makes a huge difference. Once your walking unassisted, stairs don't make you look for another way to go, swimming for a couple of hundred yards is not a problem, and last but not least, climbing a ladder with 80+ pounds of gear is doable on a pitching, rolling boat and that leg has the strength to keep you on the ladder, I'd say your ready. There is less strenuous diving, and I would ease back into it. If you boat dive ( I know nothing about Pacific NW diving) I would remove my gear in the water and hand it up if possible before tacking a dive ladder. It seems like it took almost a year before my knee felt "stable". I still "one leg" ladders and stairs without a handrail. If currents are an issue, I'd make sure you have the strength and stamina to handle it if needed. Split fins are supposed to help, but I don't use them.
A physical therapist that dives could probably work up some excercise that could help strengthen dive related muscles. My last PT compared my bad leg to my good leg on strength and range and when I was within 80% or some percentage, he released me.
good luck, what ever you do, don't bite off more than you can chew right off the bat. You, and your buddy, could have a very bad day.
jay