Win or lose, who cares as long as you can still get some pvp in. If your team sucks (which is almost all the time for me since merge), just stay with the handful of players that are decent and get some kills. Even if you can't get the win, you still get pvp. Unless you play games just for badges and tokens...
Now, if your getting farmed at the base and at the other spawn, then just leave, because that's not pvp, it's just a sh!t mini that was over before it begun. No point to stay and inflate someone's kills because your team is down players.
A single demo can only carry a team if they have some help during the large fights where they can AoE, for the most part your not going to Rambo out by yourself and make any difference, unless the other team is complete crap and let you do what you want.