how much can you get after tax? try finding a way to reduce the tax on capital gains
what is your utility of this money? It's not the same if you are already a millionaire or if you are broke, if you want to make a family soon and chill or if you want to keep working, if you can find a job paying 400k per year, etc.
how risky is the business? you feel like it has good odds of failing to scale up so if you have no other asset, it feels better to sell
can you find a middle ground (e.g. keep some ownership and control, to reduce your exposure, maximize your utility and your future profits)?
It all comes down to: