I thought about this too and I'm not worried.
Well #Bitcoin either succeeds or fails 😇
But if it succeeds most WW value transactions will be on-chain and be of rather high value and if you check the number of transactions being made WW be a lot and those will be able and willing to pay substantial fees.
Besides that #Bitcoin will be just as much needed as current financial payment systems, so big players and Governments will make sure it is running secured and stable.
Those two combined will should be enough!