It is already a sunk cost if they just bought futures, so shouldn’t keep them from flying. They can take delivery to fly, or sell for someone else to take delivery at the low price.
The hedge must be more complicated to explain why they would stay grounded.
Hmm. I don't think the hedge is that complicated, so maybe it's not particularly relevant after all. I was just thinking of it in terms of complementary goods -- normally we'd expect suppliers to increase output when the cost of an input drops, but in this case they already ate that cost so the effect would be damped. But maybe not?
I suppose there's also a question of how long OPEC floods the market. But IDK, and you make a good point.
The hedge must be more complicated to explain why they would stay grounded.