Thanks for your answers, I understand that it is really unlikely that this will happen but wouldn't there be a way to improve BTC's algorithm to consider a large and fast variation of its hashrate (maybe with an average time of the last 50 blocks or any suitable system), some kind of security system to prepare BTC to fight against any eventuality. It seems that Ukraine has been without electricity for a few days and we can see a quite big variation in the hashrate of BTC since November 22nd, I don't know if it is due to Ukraine but we can imagine a situation where Europe and USA would be deprived of electricity and that would cause a big problem in the hashrate. Since 2009 this situation has not happened but the more time passes the more likely it is to happen, especially with the recent news. Another nice solution would be to better distribute the miners geographically but I'm sure that will happen over time, maybe even placing some in orbit.