Well, it is "sort of" bad etiquette to just drop the game with no warning though.
The problem is, in Dom, adding in an AI dramatically changes the way the game is played. It's generally considered to be a large advantage to the neighbors, since the AI isn't as clever at waging war, so can be easily annexed. On the other hand, it's also a serious problem for anyone with much of a border who was NAPed to that nation, as the AI may start rampaging at any given moment, they love raiding.
But at the same time, if you offer the nation for a sub, often someone will join just for the challenge of the unfavorable position. As you just pointed out Fakey, it gives a great chance to try out something wacky and risky, for the fun of it.
So in summation, don't just randomly drop out, it's not nice.
