There is not much you will be able to do with the footage, if you have already tried adjusting the levels in post you pretty much don’t have any options. If this was my footage I would open up my waveform monitor and get my levels below 100 IRE and add some contrast. Because the highlights are so washed out the camera wasn’t able capture any detail. This is why I hate DSLR’s for video or at least as my primary camera. I don’t personally use a 7D but I have heard about people using Magic Lantern as a way to help monitor your DSLR footage and lets you know when you are peaking while shooting. The footage also looks better when zoomed in because your lens doesn’t have a fixed aperture, so when you zoom in less light enters through the iris. Look at purchasing a f2.8 lens.
Stage lighting is very tricky to work around. If you are doing more of this work in the future look at purchasing a used HVX or HMC-150. You will have zebra’s and the ability to monitor your footage so much better.
Good luck!
Micah