Rob. Im about to have my first kid, a boy, and cant even imagine what it must be like to recieve that kind of news. I've done it to my parents twice. Once with a broken arm and a second time with a shattered heel and broken back. I hope to never have my parents go through ot again.
Your sons probably heard this a lot, but his leg will get better year after year. Its been 4-6 years since my accidents and Im almost 100%. And I limped for a while. Just keep his spirits up, do some light strength training, and stretch, stretch, stretch. Accidents like this do a number on tendons.
Best of luck to you and your son. Nice looking bike too.