Let's talk about horses who sustain a suspensory injury -- in my case an 8 year old with a minor tear, but still needing 6 months off. What are thoughts on how many horses can come back from these injuries and have long successful careers versus the percentage that end up re-injuring the same area or another leg? I seem to hear quite often of horses that end up re-injured after a year or two of returning to barrel racing with new tears. If this is more than likely, I want ot sell my horse as a trail horse now, instead of trying to bring him back!  He's too sweet to go through this again. Thoughts?

I have rehabbed several suspensory injuries.  So far, all have come back 100%. I have a really good vet that has a great u/s machine and I do regular  cks every 4-5 weeks to make sure they are healing. 
scar tissue is definitely not as elastic as regular tissue. Constant, therapy to improve blood flow, along with PRP in the lesion limits the amount of scar tissue and promotes the regrowth of healthy based tissue. A supportive shoe, especially if it's a hind leg is necessary.
Things that will decrease your odds of a good outcome are:

lack of ultrasounds to monitor, gauge and adjust therapytoo much movement, too quick

just turning out the horse and letting him stand (very bad)

Because of the metabolism and lack of blood flow in the area , modalities like lasers, Acuscope (my favorite ) are needed to help the area heal and not remain stagnate. 

They can come back 100% sound, but the structure will never be 100% again. The scar tissue will have a greater risk of tearing than the original ligament tissue. Also, with a tear 6 months is best case scenario, I'd be prepared for 12. If rehab and the therapies listed above have been followed meticulously, you might be back to riding in 6 months, probably not running. Tears usually take 12 months to return to full performance in most cases. You'll also have instances of setback, I just had one with mine that strained a tendon. She was origianlly set at off 4 months & thats with no structure damage. We stepped up her exercise load and the inflammation went back to the starting point more than 2 months into rehab. Luckily still no tissue damage. It never goes exactly to plan