I don't wear the dailies for practice personally (eyesights good enough to train without them), but when I'm out airsofting they stay put despite me running/jumping etc, although i don't have the solid ones so i can't comment there. As for self defence I've never really conisidered contacts as opposed to glasses, but as i believe someone's already posted I'd probably be more concerned with defending myself/defusing the situation than taking off my glasses.
Daily contacts for me dry out to quickly. I put them on at 8 in the morning and they wouldn't come other until 11ish at night. After 12 hours they just started hurting. With bi-weeklies they are good for 16 hours easy. I get a lot use out of mine.
Yeah i have to say never used them for longer than 8 hours, i guess that not being able to use them for long periods of time could be an issue for people.
I wear mine for about the same time, 8 till 11, and have no problems. Just depends on the individual I'm sure.
The key, as you point out, is the proceeding stages. Once it becomes apparent that escape or deescalation aren't viable options. striking preemptively and not allowing them to "get a go" will mean your glasses won't be an issue.
You can buy unbreakable frames, and plastic lens, or just take them off in public/when out. I don't wear mine when "out out" but they're mostly for close up work, and if I was doing close up work when "out out" I'm sure my partner would have something to say!
I'm as blind as a proverbial bat. If I removed my glasses or had them knocked off, I could see a person near enough to me to fight them but I'd probably miss seeing a weapon and situational awareness would be seriously impaired as it would all be a blur. Not a lot I can do about that and just as well that I don't live in a particularly dangerous area. My last real situation was back in the early 80s. I was on the upper deck of a bus and the first thing I knew was a kick from behind that smashed my glasses into my face. Minor cuts - missed my eye. (Incidentally, TKD saved me on that occasion as I threw a kick or two then got my back to the window and used the seats either side as cover. Protected my head with my hands and they threw a few more kicks and punches and ran off. )