There is no telling what might have happened if he had been driving
faster.
There was no telling what might have happened if he had been driving
faster.
The time of the if-clause (had been driving) allows for both present and past in the matrix clause. You could be describing, today, yesterday's accident ("there is no telling"). Or you could be narrating a story set in the past ("there was no telling").
The ice on the river is thin. There is no telling what might have
happened if he had taken another step.
The ice on the river was thin. There was no telling what might have
happened if he had taken another step.
From a narrative perspective, in the second sentence (was thin), you would still have both choices open to you.
The ice on the river was thin. There is no telling what might have
happened if he had taken another step.
The ice on the river was thin. There was no telling what might have
happened if he had taken another step.
Choosing the present ("there is no telling") would cause the narrator to be speaking directly to the audience about events that took place in the past.
Choosing the past ("there was no telling") would be used when the center-of-consciousness is relocated to the past, as for example when one of the characters in the story becomes the implied narrator. Then we are let into the mind of that character, rather than into the mind of the narrator.
Complicating things further (or making them simpler, depends on your point of view), the "character" who is thinking the thought "there was no telling" could be the narrator (the speaker) simply remembering himself back at that scene in the past.
Narrator for our purposes here means simply "a person speaking about the past", about past thoughts, past events, past actions, whatever.