Wow, Bucky. First, my condolences to you and your loss. What an absolutely horrible experience to go through.
Hats off to you for coming as far as you have with everything you've had to deal with both emotionally and physically.
I don't have any advice on how to let go of a sport you love doing. I suffer from an autoimmune disease that when it flares up, pretty much makes my life miserable - all my joints "hurt", I'm tired, I lose my speed and endurance. Really set back my triathlon training for this season as I spent much of the first four months of this year just doing whatever I could, but not able to "train" much. Fortunately for me, I'm not in pain like you are. Although, I "suck" at whatever I'm trying to do at the time, I can still do it. Takes me longer to hike trails, can't ride as far as I should be able to, affects my breathing, and my softball ability goes out the door (as a shortstop, I need all my wits about me, especially as a female playing on a coed league!

) But I've never had to stop any of it.
....you know, thinking a little more, I did give up something I loved. I sold my motorcycle at the beginning of this year. I didn't ride much of last year at all as I kept getting more and more ill. I was (still do sometimes) losing focus more frequently, I'd get dizzy (I have really low blood pressure as it is, but it would drop for no reason), and the vibration of the bike made things worse. I couldn't feel my hands and feet, so braking and shifting gears became difficult, as did stopping and putting my foot down. I was just too scared to ride anymore as I felt it was just a matter of time before I had an accident. I guess I traded motorcycling for something else - more bicycles

Seriously, before this year, I just rode around on our trails at a leisurely pace and commuted to work. Don't get me wrong, I rode a lot, just not competitively or with groups. After I sold my m/c I bought my Fuji Cross Comp - I had never had a road bike, and we have lots of dirt trails around here, so I wanted something that could do both which is why I got the xc bike. Riding became a whole new thing for me, I've competed in two tris this summer, with one more on the way, I "work" for a my LBS as a group ride leader on the weekends, and I'm planning on trying cyclocross racing this fall. I borrowed a girlfriend's mountain bike and did a mtb race a couple weeks ago and loved it!! So I'm getting more of that kind of riding in. I suppose it's just a matter of finding something that you enjoy as much as you do running. With your cycling and swimming, you shouldn't have to worry about putting weight on, and it will keep your joints moving. That's all I've got!