The match doesn't end when everyone leaves anymore? We had a friend in a 5 stack lose Internet and hoping to avoid the party abandon, we all left. The game never ended and we all got an abandon. The enemies had to kill our ancient, which took them 10 minutes after we left to do so...
A+ system Valve. A game we would have played until the end 4v5 ended up with everyone wasting their time and a team having to push against nothing because we didn't want an abandon, and ended up with one anyway...
Yes it does work, I did it very recently.