Why would Signal stop accepting European phone numbers? It’s not like they want to leave the EU, they can just continue offering their services to EU users, but they can’t have servers or offices or any legal entities in the EU if they get banned. That’s not such a problem, you can access Signal over the internet from anywhere in the world, and if EU states start blocking Signal, you can still use Signal TLS proxies, good old VPNs or Tor. Edit: Signal is also banned in Iran, but they of course accept Iranian phone numbers, as they don’t impose the ban, the Iranian government does. You don’t really have to worry about this, I’m sure Signal will do everything in their power to continue to operate, even in jurisdictions in which it’s banned.