Mostly what others have said. I know the official stance is to never leave its presence. I second what @nystromd said. I use a $25 Wyze camera and can watch/listen on my phone. I also scale my willingness to leave by my calculated risk. Bigger bit, full depths of cut, possibility of my tape/glue hold-down failing? I stay put.
If I’m clamped, have run the job before, and am only doing shallow depths of cut, I’m much more forgiving. For example, on the final passes of these cnc photos, I’m taking like 0.03in or so with a 1/8 and 1mm. I’m really not worried about this. Minimal removal, minimal forces, minimal dust (if there was going to be a hot router/dust fire issue).
I would never dream of leaving my house, that’s for sure. Most of the time, particularly after seeing some fire reports here, I don’t leave the room. I have bluetooth hearing protection and watch youtube videos/hunt on Craigslist/Amazon to salivate over things I won’t buy but dream of 
Edit: and, meant to add, even when I think nothing will go wrong, I’ve had a bit slip from the collet and start eating into my t-track/wasteboard. Glad I was there to stop it! Also, when doing tons of boring operations to make a threaded wasteboard, I didn’t realize that my cut was just at the limit of my lower z travel. I ended up driving the z carriage off the freaking rails (the bottom rollers came off the v-track). Holy crap good thing I was there for that vs. the router going hog wild with a 1/4 spiral big and flailing all over.
Maybe key point is: no matter what we think we know… you can never know for sure. No one can sign off on you leaving. Obviously if we knew an “oh sh*t” moment was going to happen… we wouldn’t leave. The very fact that everyone’s stories of “I’m glad I was there” or “it was horrible I wasn’t there” are going to amount to unexpected issues. So, if you want to leave… accept those issues/risks. None of us can sign off on this for your peace of mind! It’s your own decision based on what can possibly happen, and the damages that might result.