If you successfully defend both towers, as I outlined above, the chances that they will kill your general are very low because it means they have to offtank two WMs, and your general's health and dps are VASTLY increased. I've done what I outlined about 30-40 times, and only one time have they been able to kill Drek with 2 WMs still up.

The only really valid strat to winning for them is to send a team back to get those towers. Premades will do this (and honestly, you're not going to singlehandedly beat a good premade), but pugs virtually never will, or at least not with enough people to kill you. And even if they did, if the rest of your team isn't just following you around, they have a big lead and should easily win it.