...A trojan walls you into a corner?
...On Vanaduke, a Shadowfire block spawns inside you?
... The team you're playing with is dying every half second?
... you've D/c'd and wanna improve the odds that you don't die?
... your connection suddenly goes from 3 bars to 1 bar because of a major lag spike?
The trojan is actually easier to deal with than you might think, a simple shield bump is usually good enough to grant enough leeway to escape. If your shield is broken, I've noticed that the blitz needle line knocks it back enough too.
I don't think there's really anything to with the shadowfire situation, as far as I know, mostly stay out of the light patches in the first place and pray that your team members get some water to you quickly.
I usually try to stay on even if my team is bad - sometimes I'm the bad one, and I appreciate the help I get from more experienced players when that happens - but if they're so terrible that it's involving losing all my health to rezzing, I usually just go solo.
I've found that if you've d/c'ed and you type something into the chat box, it'll kick you out of the game and you can log back in fairly swiftly, or at least moreso than if you just waited.
Shield and hope?