[0] https://terrapass.com/blog/carbon-footprint-of-driving-vs-fl...
We shouldn't be comparing the most optimistic outcome in the world as you'd prefer it to be that could happen as a result of the flight being cancelled, we should be comparing the most probable outcome in the world as it actually exists.
I would put a good $25 on there being almost zero flights in the world where every passenger has no relation to every other passenger (to the point where you'd need N individual cars to transport them.)
I'd add another $10 on top to bet that there isn't a situation where all of those passengers would refuse to get on a train / bus / coach with the others if the plane wasn't available.