If it was a straight cut - ie the engine ran down - I'd dump
Is a straight cut an emergency or an urgency situation - would you call mayday or pan?
At first I though it seemed a bit contradictory to call mayday, and then take the time to go out dumping fuel. But, the fuel dump is (primarily) done to ensure sufficient performance for a possible G/A (appch climb) - so perhaps the surrounding terrain clearance should also be considered.
So maybe the situation is considered to be critical enough for a mayday - but the crew still decides to dump fuel to increase performance.