It's ridiculous to expect anyone to stay forever, but you should both agree as to what is a good period of time to be vested. Probably you should have agreed on

It's ridiculous to expect anyone to stay forever, but you should both agree as to what is a good period of time to be vested. Probably you should have agreed on that in advance, but now you have to give and take and agree to compromise on something that works for both of you. Also, this guideline would be good to help others to be vested in the future. You have to consider what works in the industry.