A player should be prevented from matchmaking for a certain time like 30 seconds or a minute if they leave a match lobby. People leaving is really annoying because it screws your squad over.
For all those people who are going crazy about how you "can't get any money," you actually get money after each wave. Not for each kill, which makes sense. Some random guy you kill isn't going to have a wallet full of money for you to loot. Funds are coming from the city and they reach you between waves.