What would it mean if someone were to successfully exploit these? Most or all L2 ecosystems or the magic components that let them speak to each other would need a hard reset?
Every node that uses this library to validate would lose synchronization with every other node (if we take them at their word that it's not a monoculture), the bigger half would be considered "correct" according to how blockchains work, if it's the non-exploitable half - just lots of wasted resources and longer settlement times, if it's the exploitable half - illegal transactions would need to be reverted by agreement of the community, which is some sort of reset.