Work during work time, don't work during not-work time. Good practices mean that everyone is important, but nobody is irreplaceable, the team and the work will move along a little slower, but that's fine.
"If I see you log on, I'll disable your account."
Personally I’m sure I’d forget to sign out of something.
Some people are just workaholics and need interventions to actually take a proper holiday.
Real engineers think about handling things when stuff goes wrong, not "everything will be on the happy path forever".
Yes, there are constraints, but to me this sounds like an unacceptable level of exposure.
The only people who should suffer this much are the true busines owners.
But... That's not how days off work.
My manager doesn't stop overworking. When told on peer performance review that we have people who are consistently overwork because they are swamped, he played it down.
But hey, at least he doesn't encourage overworking either.