If they expected 30 years of service in the first place, then they should've put a 30 year vesting term on the shares from the start.

There's no right answer, it really depends on what people want and negotiate for. I may expect to put in 5 years and then retire with whatever value we end up with. That's totally reasonable. Just because my partner decides at that point to keep working doesn't mean our deal is suddenly no longer valid.

That's why I say, if you want to change the deal halfway through you need to get the board to issue more shares.