There are TONS of other exercise options! I can't run on the treadmill anymore because of my knees. However, if I put it up to a good incline and turn it up pretty high, I can get an excellent workout just walking! I also swim and do water aerobics for more cardio.
And you didn't mention lifting, trust me you can burn quite a few calories doing that too! The best part is that while your body repairs the muscles you tore during a workout it continues to burn even more calories. Not shabby!
Also, I hear you on having problems sticking to your diet when you can't do your exercise of choice. I used to be like that too. Thankfully, I just learned to separate the too. It's a good thing too because I've been sick a lot this past year so I haven't always been able to consistently workout.