In MM leagues thats simply not possible, a 5 minute timer is ok there. I remember a guy once trying to disconnect and reconnect permanently from turn 12 on after he saw that he would loose the match, dragging it on and on...
Those kinds of silly "Auld World" behaviors (i know there are much better MM leagues out there, its just an example) has to be controlled by ristricting the possibilities for such things. So that 5 minute timer should better count for a game and not for every connection loss.
Which is why I suggested a total time limit, Allowing a maxium of x minutes of "Disconnected time" thoughout the game so the worst they can do is make you wait that time out and no more. (With Dcing and Reconnecting could be ages depending on how good they are at it)
I suggested 20minutes because sometimes there could be a blackout and might take someone more then 5 minutes to restart there computer login start BB rejoin game etc, But not up to us to find a sweet spot the concept is still good imo.