I need my body to be healthy for what I do, so I take my healing very seriously. Whenever you get any joint sprain, it's wise to avoid using the joint for the first 48 hours, a vital period of your healing. I didn't even go into the dojo for the first 48 hours so as to avoid standing on my bum ankle. After that, I resumed teaching, but tried stay off my ankle as much as possible as I did so. Even when I was just standing around and giving advice, I did feel sore by the end of a class at first. Jenny, my doctor student, gave me some exercises to strengthen the joint gradually over time. I've been religious in doing them. And last night, I was finally ready to get back to the mats and train.
I'm still not a full capacity though. Running and skipping are still stressful on my ankle, so I had to do my own warm-up independent of the class. I did 5-10 minutes of shrimping and crab walking rather than participating in the classes usual running exercises. The only other thing I had to make modifications for was forward stance (zenkutsu dachi) practice. When my injured ankle was the back leg in the stance, I had to do a modified half stance to avoid stressing the ankle. Other than that, I was able to function completely normally in class, which is great after 2 weeks of doggin' it! :)
Anyway, sometimes you have to back out of training to let yourself heal, but in some cases you can get back to training in a limited capacity if you're diligent about avoiding things that will could hamper your healing. If you do decide to get back to training, make sure you do so under the guidance of your doctor so you know what types of movements to avoid. Some people, however, just can't participate in a class and hold back in any way. These people are probably best served by waiting until they're fully healed before returning.
Have you ever had to train around an injury? What adjustments did you need to make to allow you to train?