You can't do anything about it, other games tried crap like this, and ended up punishing legitimate disconnects. (CoD BO2 for instance) My friend was on a game when a power outage occured, sure he only got "banned" from playing online for a minute or two, but it was completely stupid for his "first offense on DC'ing" as they put it.
While power outages are unfortunate, I completely disagree with the "legitimate disconnects" argument for opposing DC punishment. And, pending the circumstances of your friend's power outage, he might have had that coming also.
If your internet is unstable enough that your router likes to hiccup and boot you or otherwise regularly provides a poor online gaming experience, you should play offline exclusively.
Having said that, I support measures that aren't really that extreme- display all disconnects, intentional or otherwise, as a "DC" tab in an opponent's profile/record before a match, and give people the option of refusing a battle at that time.
If your disconnect count is more than 50% your wins and losses combined, your file is automatically disqualified from any tournaments until that number changes.
Matchmaking could easily be programmed to pair high DC counts with each other as often as possible, since neither player is likely to honor the other. --- An infant sea turtle is actually capable of killing an adult African bull elephant. It does, however, require a substantial amount of surprise.