My plan is to start with easy miles and keep up the spinning and swimming so that I can get some good high heart rate work done without the impact. I plan to start at about 30-35 miles per week. If that goes well for a couple of weeks, I'll replace one of the spinning sessions with a tempo run. I plan to do a 5k as a fitness test some time during the first week of August (maybe Sunset 5k in Sheffield or Dog Trot in Huntsville). That will give me an idea of how to pace my workouts as I train for the Rocket City Marathon this fall.
While I've been out, I've really tried to avoid losing ground by doing weights, core, spinning/stationary bike, and swimming. I spent over an hour in the pool yesterday! It's a 25 yard lap pool, and I did 25, 50, and 75 yard intervals. I just can't quite last for 100 yards yet. I was pushing really hard, was gasping for air, and nearly puked. But still, it's not the same as busting out a set of hard intervals at the track.
I will say that swimming is humbling! I'd like to keep practicing, though. Who knows, one day I may try a tri.