Startups have high turnover. The reasons are both due to the nature of startups and the nature of the people they tend to attract. Specifically, startups are bumpy rides where the bumps can throw many people off the ride, and they tend to attract people who are too restless to stand still in one place for an extended period of time.
As a result of this high turnover, when you work with a startup, you eventually develop a wide network of people who go on to roles outside of the startup. And many of these roles are once again in the startup community. You eventually reach a position where you know more people outside the startup than in it. In other words, you know more people who have left the startup than people who continue to work there.
If you hope to retain the option to continue to work with the people who have left, it’s important to part on good terms. This isn’t always possible, because it requires that both parties leave on terms where they believe that they were treated fairly, or that a party who believes that they were treated unfairly chooses to part on good terms despite this.
Not everyone is prepared to do this. However, it’s worth doing for the part that’s in your control.
From the perspective of the employer, this means things like agreeing to serve as a reference for the employee in the future, or at least not speaking poorly of them unless there’s a very strong reason to do so, and not nickel and diming the employee’s exit terms.
From the perspective of the employee, this means things like continuing to work hard until the day you leave, transferring your workload to the organization or another employee who will take over your responsibilities, and not speaking poorly about the organization following your departure.
I’ve seen both good and bad departures. The former sometimes produce new opportunities which carry more value than what the original appeared to hold at the time. The latter don’t.