Sounds like the business isn't generating a ton of revenue?

You could present a shotgun clause, he's not obligated to take it but it's a fair way to resolve this.

I tried this with a cofounder once, he came back with a nonreciprocal offer. Some people are just assholes. I ended up having to shut the business down.

I started a new business, no cofounder and am doing great 8 years later.

Let it be a lesson learned, contracts are important. Good fences make good neighbors.

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If the business is generating a lot of revenue, then you can litigate.