Yeah, I would definitely say that some warnings like that could help the "adequate communication of peril" if it wasn't possible to make it clear that there's danger. If the player clicked twice on the outlet with the fork, yeah, I would definitely say that some barbecue was in order!
And yeah, autosaving has been used in a bunch of games. I usually see it saving at the start of certain events or based on the player entering a new area. I can't think of any games that just saved every five minutes, though. There might be an issue with that though, for example if there was a timed puzzle like defusing a bomb, and you were two seconds before the bomb blows up with no chance of finishing and then the autosave kicks in, so when you die and reload, you'd just die again with no chance of saving yourself. So, you would have to be careful with a timed autosave, turning it off in certain situations, but it could probably be used to good effect. I still think that the first two ideals I discussed need to be followed at all times, even with an autosave, though.
And yeah, autosaving has been used in a bunch of games. I usually see it saving at the start of certain events or based on the player entering a new area. I can't think of any games that just saved every five minutes, though. There might be an issue with that though, for example if there was a timed puzzle like defusing a bomb, and you were two seconds before the bomb blows up with no chance of finishing and then the autosave kicks in, so when you die and reload, you'd just die again with no chance of saving yourself. So, you would have to be careful with a timed autosave, turning it off in certain situations, but it could probably be used to good effect. I still think that the first two ideals I discussed need to be followed at all times, even with an autosave, though.