As an American, I would definitely use poorly in this context. But since it seems they're an English speaker learning French, I think it makes sense to say badly. It's a more direct translation for mal, the word they're learning
If it didn't happen at work and it was a first time offense, I could see a company putting him on a leave of absence pending completing rehab or something similar. A lot of companies have started viewing drug abuse as a health issue and will work with their employees a little bit. I don't think they generally give many chances though
Hopefully the discharge is honorable and their service helps them get a good civilian job where they are happy and accepted