What happens to the IP when the company is shut down?

That is the million, or in some cases billion, dollar question. As Steven stated, what you describe which we call "intellectual property" is property, i.e. assets, that belong to the business and need to be disposed of or allocated as would any other property acquired by that business during the course of its operation or start-up. Ideally, as Steven, the disposal of this property was addressed in an agreement or Articles of Incorporation when the company was formed. However, as lawyers who often get to these situations only when the fire is already burning and needs to be put out, such an agreement or bylaws typically tend to be nonexistent and what you describe about one or more founders/partners/shareholders taking the property or know-how and working on it on their own is common. And once one or more of those founders make money with the IP to the exclusion of the other(s), that's when the other often gets upset, sues, and a huge mess ensues. So hopefully, if that agreement or arrangement is not yet worked out, it can promptly be worked out ASAP before the parties find themselves in litigation. A good corporate lawyer in the relevant jurisdiction should be consulted ASAP.