Eh, I think everybody needs to take a second to realize what they are asking for...
I think a better solution would be, if a player leaves in the beginning of an RA/AB, since there is a nice 50 second grace period, wouldn't it just be better to, for RA, for example, to grab a random player already waiting to join and just insert them into the team that had a player leave or disconnect?
For AB, if you have somebody leave because they are down 50 points, that's just something you have to deal with. It's not like you were handicapped from the start... They were there fighting, and trying to win. They just gave up sooner. Life's full of disappointments...
For the leecher problem... I don't have anything as of now. I'll edit in my possible fix to that when I think of it. :P