Reducing a sentence

Consider the following sentence:

• [We have to make] one more effort, and [then] we will rest!

Can the first and second clauses be reduced by removing what is in brackets?

The result could be:

a) One more effort, and we will rest!

Or

b) One more effort and we will rest!

If b) is right, it seems that there is a non-verbal expression in a) before the comma, and, therefore, perhaps should not be a comma in order to integrate “One more effort” in the second clause.

However, the comma was correct before reducing the parts of the sentence that were in brackets.

I will appreciate your clarification about whether a) and b) are grammatical and idiomatic or not.