The notion of asking for release from a collar is essentially a protocol step. It generally doesn't happen in long term relationships, and definitely not in relationships that don't end amicably. Those relationships just end and the people involved move on as best they can with their lives.
So asking for release is the reverse of being collared. Much consideration generally goes into accepting a collar, and that same amount of consideration would also go into asking release from one.
If a Dominant refuses to allow release, they have discounted the consensual side of what we do, and should be ignored and shunned from the community.