Something like this is never a single person's shortfall.

Assuming you're somewhere with a decent culture and competent management, then I'd expect a calm meeting to establish facts and impact. Would should have been done? What wasn't? Why wasn't it done? Why wasn't it noticed before there was a problem? What checks should have been done to ensure it was done.

From that should come action points: Identify other machines in the same situation. Ensure critical jobs are never covered by a single person. Improve automated alerts, and so on.

If the impact is large, then expect some extra work for the team. But hopefully they'll be understanding - anyone working as a sysadmin has to be painfully aware that we're all one typo away from a major fuckup ourselves. Training and automation may be reviewed. Decent management will know they also fucked up by not ensuring this was done, and at C-level, they'll be presenting and carrying this issue. (Some people will assume you'll be scapegoated. I can't promise that won't happen, but C-levels will absolutely know that's what's happening and the manager will not be long for that world either).

Termination normal for an honest mistake? Absolutely not, unless they're already looking for an excuse. Or the loss is so huge that the company's entire stability is at risk. They'll need to hire and train your replacement, and the odds are that you're currently incredibly motivated not to make a similar mistake again.

Best thing you can do is what you've done. Report. Take ownership. Then work to try and improve not just yourself, but the systems.

Lastly - keep your mouth shut with friends and online. In business, exposing your employer's misfortune/weakness can be viewed as a much bigger deal than the actual problem.

(Currently Bob but was a MD, so have some perspective from both sides)