That has already been taken into account: the amount of energy used in mining due to the PoW algorithm would be so huge if the price continues to surge upwards, thus posing a problem not only for the infrastructure needed to be built but also to the end product of using all those energy. Switching to a new algorithm would be nice, albeit poses a different problem like the older one. It's a hard transition, but in order to balance everything, something needs to be done first. PoW wouldn't be around for the next 100 years for bitcoin. It will be replaced with a newer, more effective and efficient algorithm eventually.
If the energy demand continues rising, the probability that governments step in is high. As you said, it would threaten the whole infrastructure or even pose a risk to the national security.
Plus, it is easy for the government to find places which have a high energy demand. So future regulation regarding mining is very likely.
In my opinion, it may not be the worst case for the bitcoin community because private mining would maybe become profitable again?
Best regards
razielnkain