So, this is ok if the payout in 4. is sufficient compensation for the existence and effort you put into the company.
If, 4. is a desperation move, and you're hoping bigco is going to help your company reach heights you're unable to reach on your own, then you're rolling the dice.
I've had exactly this experience. The founders expected BigCo to take them to new heights, but eventually bigco dismantled the company piece by piece.
Literally the economic winds changed slightly, success wasn't immediate and so the BigCo CEO got all excited and went off chasing something new and shiny.