So let's say, I started a random game, someone rang the doorbell, so I quit the game dealing with real life things first, you want me getting ban on this?
Such insanity.
I don't think (or at least hope) that anyone is advocating for "drop = perma ban"; however, most modern games do have a "cooldown" period for leaving that increases the more games you leave.
For example, this is CSGO's system:
First cooldown (level 1) - lasts 30 minutes
Second cooldown (level 2) - lasts 2 hours
Third cooldown (level 3) - lasts 24 hours
Fourth cooldown (level 4) - lasts 1 week
A week of clean play will reduce an account's cooldown level by one.
In your example (if you were playing CSGO) you'd receive a 30 minute ban from competitive play. However, if you DC'd again within a 1 week period, you'd receive a 2 hour ban the 2nd time and so on. A week of not DC'ing (or just not playing) would then lower your "ban level" by 1.
Personally, I think the above system would work with CoH2 if it were approximately 1/4th as severe. So the first ban is around 10 minutes, the next 30 minutes, the 3rd 6hrs, and the 4th being 2 days, with it decreasing by 1 level for 2 days of "clean" play.