If that won't happen, we'll have no choice

Question

The decision has been made and we ask for just one thing, an immediate positive intervention of Zaccagnini. If that won't happen, we'll have no choice but to execute the sentence, you understand?

This is the part of a monologue from the movie The Moro Affair. I would like to ask whether the clause "If that won't happen" is OK. I am aware that in some cases there is needed to use the future in the if-clause, like "If it will help you, I will go to a dentist with you". But my sentence contains after all type 2 of the conditional where the pattern is: if-clause – Simple present and main clause – Simple future. So I would await "If that doesn't happen, we'll have no choice".

Answer 1

'If that doesn't happen' is the right form.

'Won't' comes from 'will not', so applies a person deciding not to do something. 'Doesn't' comes from 'do', so just describes a circumstance.

You might use 'if you won't' or 'if it doesn't' but not 'if it won't.'

Edit

Just realised it is more complex.

'Will it happen' and 'it won't happen' and 'it will happen' are all fine, but they never get combined with 'if'.

So

will it happen?
if it doesn't, we'll be fine.