Had a ranked game recently where my Bot lane got absolutely demolished. I also made some mistakes which didn't help matters and our Mid laner was on tilt starting in champion select and my mistakes and our Bot lane's destruction didn't help their state of mind to the point that they were making poor decisions like diving in on a lost causes, which in turn caused our Mid lane to give up and AFK for a good portion of the game.

1. Even if the game is ranked, you can dodge if you see signs of problems in champion select. It will cost you 3 LP and 5min+15sec time penalty. Which is a better deal than the -16 LP you are probably going to lose. If you end up dodging a second time it will cost you -10 LP + a 30 min time penalty. That is -13 LP so it will probably still be less than you would have lost via actually losing a match. Though if you are in promos a dodge is an automatic loss, so the mental math gets a little trickier.

2. You can't tunnel (this is usually bad even if your are ahead, but if you are ahead you have somewhat higher odds of getting away with it). You have to take the scraps that they feed you. E.g. if their fed ADC tunnels onto your support to the point that he takes 3 tower shots trying to kill your support, getting a shut down on him can be huge for your team, but only clean up their support at the same time if it is free. Don't chase their support through an unwarded bush if you don't know where their jungler or Mid laner are. And most definitely don't chase through a second unwarded bush no matter how low they are. 3 second rule on chasing if you have vision of them. If you can't catch them in 3 seconds then back off.

3. If you've probably lost, practice playing from behind. Ask yourself things like:

How do we establish some vision?

Who on their team do we have to tag team because there is no way we can 1v1 them?

Is there a way that we can force them into making a mistake (can I goad them into turret diving or get them to chase a slippery team member?).

If we do get an opening, how can we most productively use our time?