"Most importantly: how do I best stand up for my own interests here, without being the asshole that ruins the deal for everyone?"
You're one of the few people with the experience and know how to take the product quickly to whatever direction the new owners will want to take it. That's worth money.
That would be the angle I would play if I were you.
How much it's worth is a trickier question. Personally I think it's worth a premium, but only if your company doesn't have lot of people with the same expertise and assuming they want to keep developing the product.
If it's a pure acquihire situation, the product and your equity in it has no value. Your value is what value you personally bring to the company.
You're one of the few people with the experience and know how to take the product quickly to whatever direction the new owners will want to take it. That's worth money.
That would be the angle I would play if I were you.
How much it's worth is a trickier question. Personally I think it's worth a premium, but only if your company doesn't have lot of people with the same expertise and assuming they want to keep developing the product.
If it's a pure acquihire situation, the product and your equity in it has no value. Your value is what value you personally bring to the company.