I run into this at least once during a couple hours of Crucible play--several times this weekend, already. After players quit games, leftover teams are [b]very slowly[/b] repopulated. Even if players abandon the game during the first few minutes. Meanwhile, there's 2 on 6 control--it isn't fun, at least for the 2. Those are very long minutes. And these disadvantages go on for most of the game. It seems futile--yet humorous--when the game finally repopulates during the last couple minutes, and the new players barely get a few kills or steal a control point. Games with 4 on 6 are pretty common, and those seem even less likely to be repopulated. Luckily, those game aren't just forfeit for the smaller team. In my experience, they usually still have a chance. You should be always feel free to leave if you have something urgent to complete IRL or you just rage quit, but not with impunity. For the quitters: the Crucible could be locked for a period of time as punishment. For the leftovers in game: there could be an increasing handicap depending on the number of missing players, until the game is repopulated. I really hope the importance of re-balancing teams is just a feature left out of the beta, but solved for the release. The current system does not work well.
If I am unable to open three ammo caches in a row or if I stand in front of a door and it doesn't open, but someone on the other side is able to shoot me, I leave the match. Pretty much the only time I do.