My mare severed the tendons (2 of them - 1 80%, the other 100%) in her back leg, we took her to the equine hospitial for emergency surgery. She was put in a cast that looked very much like a people cast, it was the same material actually. The leg had so much drainage that they ended up cutting the cast in half and wrapping her leg. It was a gauze pad held on by k-flex wrap then the cast was put into place and wrapped with a sticky ace bandage material. We changed it daily.
The other leg had a severed artery that had been sewn up. That leg we kept in a standing wrap to help carry the extra weight. It also helped to prevent laminitis in the good leg. We changed that every other day.
She was kept in a stall for about 6 weeks. Hand walked for five minutes a day after like 2 weeks and then gradually increased to 30 minutes (15 am and 15 pm).
The biggest potential issues that were laid out for me were infection and gang green. She was only given a 70% chance of making it with no promise of ever being sound.
There was also the possibility that she would heal but have string halt.
She survived. She healed. She is serviceably sound. She has a mechanical lameness which means that she limps but not from pain but from loss of flexibility.
You have a long rode ahead of you but it will be worth it.