Monaco is bulletproof. Italy, Britain and Germany are all fairly secure largely because of where the teams & some key manufacturers and sponsors are based. So yeah, those are all safe, I'd say. Spa is constantly under threat, saved only because it's a driver/team/fan favourite. Money could outweigh that in future. Hungary would definitely be in the firing line if a race needed cutting. Spain and the European GP in Valencia are safe for now because of Alonso's popularity, but when he retires, one of those will probably be under threat if crowd numbers fall and sponsors preferred another race in, say, the USA.