There is a good chance that you won't be able to tolerate running for several weeks. Try hiking on your mtb trails. You'll be amazed by what you see on foot that you've been missing on the bike. Also, hiking up hills will help get your heart rate up without jarring your broken bone(s). Lower body work like squats and monster walks with an elastic band will help keep your legs strong. Monster walks can be done moving forward, backward, and sideways. Anything that you can do to increase your circulation without causing pain is going to speed the bone healing, reduce swelling, and help maintain fitness.

Yes, you will probably be gun shy when you get back on the bike. It's called self preservation. Don't sweat it. Give yourself permission to walk the obstacles that you've recently mastered. It won't take toooooo many rides to regain your confidence and skills.