Co-founder exiting after pivot – what's a fair exit package?

Throwaway for obvious reasons. I’m a co-founder of a venture-backed startup currently valued at ~$20M. We raised a strong pre-seed, built a team, shipped v1, generated revenue, and recently pivoted into a related idea that I think could work—but I’m no longer the right person to lead it. My co-founder is passionate about the new direction and wants to take it forward. I want to step away cleanly and with integrity.

I have ~10% vested. I led our early fundraise, worked unpaid for months, and contributed personal capital. I’m not trying to maximize my return—but I also don’t want to walk away empty-handed after 1.5 years of building.

My question: 1. What’s a fair exit package in this situation? A formula/rule I can use?

2. Should I just keep the vested equity? Future investors may see this as dead equity.

3. Is a cash buyout common or appropriate?

How would you approach this with the board/co-founder in a way that’s constructive and protects long-term relationships?

Would love to hear from anyone who's seen this play out—on the founder, investor, or legal side.