With my agents, I tell them if and when they wish to leave, they are free to take their listings with them. People list with people not companies.
If you are leaving your present company and your listing wishes to be released, they should let that be known to your Broker. I don't believe a company can legally hold a listing if they want out.
If you are looking for a new company, would love to talk to you. Gail@GailGladstone.com 631-425-6150