Student or Learner
I wonder if there is any difference between "1" and "2".
He saved a drowning woman.
1. What if he didn't jump in? Her life would have been lost.
2. What if he hadn't jumped in? Her life would have been lost.
Only#2 is appropriate.
#1 is not possible. The first sentence refers to a hypothetical present or future non-jump, the second to a past counterfactual loss of life.