That is a good question and keeping a thoughtful eye on the machine will serve you well in the future. As for the question, I'm unaware of any hard data available to suggest which way to go in terms of adding or subtracting from engine life given that situation. However, I would be sensitive to the fact the engine will climb in temperature when you shut it off, so if the fan is running then you are in the zone where the engine needing cooling down. Now, if you are bumping up on the upper limit (210 F), fan running and pushing it very hard, say towing something or similar and quickly shut it off then will it do damage? Again, I’m unsure where the limits (actually damage the head, etc.,) but for me, I would let the unit cycle and allow the fan to stop before shutting it off, but that might be more a personal choice vs. needed.