Please consider implementing something like other competitive games where if a player disconnects or leaves a match at the start or a couple of minutes after the game is started the match is canceled.
I know ppl disconnects randomly cause of some game issue (that I hope you are aware of) and also general connection issues but you cannot penalize the whole team for one person leaving the match at the start. This is not happening rarely at least in my experience every 4-5 matches someone leaves or disconnects.