Employer offered job through CEWS or regular pay and this is what the government and employer wants. Employee needs to accept this no conditional and come to work unless they have covid19.
I am sure government and employers are encountering this right now, people happy not working and getting $2000. I would call CRA and tell them what's going on minus the firing part and ask for advice.
If you are firing him, get a good reason to terminate for previous work mistakes. Don't do refusal to come to work because they can counter with workplace not safe during covid19.