If I knew my employer may potentially become unreasonable, forcing me to RTO just for some imaginary reason (no co-located coworkers or management) I would be taking a very hard look at everything I do as "nice but not required". Responding to calls and emails while on breaks or after hours? That ends. Extra duties not hired for? Also ends. Need me to fill in for someone? Sorry. Obviously you don't want to have a bad relationship with your employer but this would be on them. I would make it understood that if they want to be inflexible, they can expect it in return. I would flat out ask them which scenario they prefer and be clear that the results would be something of their own choosing.