That can happen, but it's probably also possible to make a more risky play by either having someone tank turret and melt it down or engaging on the enemy beneath their turret.
If you are far ahead you should win that fight.
Another possibility would include heavy splitpushing, which almost always gives an opening at some point.
Or try and force fights at Baron, Dragon etc.
I know that it isn't easy and I have plenty of games too in which my team just doesn't manage to finish. But that is usually to mediocre decision making and not because there is a truly impossible situation.