If you get med sep / and or get VA benefits, can you lose the benefits by going back to work or start working?

I think I understand the question. No, you are not expected to remain unemployed if you are receiving disability compensation through the VA. I was Medically retired from the Marine Corps in 2012 and have been gainfully employed ever since. I am currently 90% and have a full time government job. Depending on the disability you will be required to go through evaluations every so often and that has the possibility of increasing/decreasing your compensation depending on what the findings are.

Depends on the work vs the rating, Better check.

Generally speaking no, but you can get a temporary rating, which will be reviewed periodically until declared as a permeant one. Keep in mind, if you are filing for 100% disability because your back is so screwed up, you can't work...and someone submits video of you swing an axe and splitting wood for 12 hours, you may lose that benefit. So don't be that guy.