if + subject + Past Perfect , subject +
would/wouldn't have +
past participle OR
if + subject + Past Perfect , subject + might/might not/could/couldn't have + part participle
Unreal situations in the past that didn't happen, with an unreal result.
If they had stayed in the country, they wouldn't have found work.
If it had snowed, it might have caused terrible traffic problems.
If he had not been late, he wouldn't have lost his job.