What happens to my IP rights when a startup is founded to commercialize it?

Nothing, “happens to [your] IP rights when a startup is founded to commercialize it” unless you take certain steps to transfer those rights to the startup. Indeed, unless you are an inventor or co-inventor (being a co-inventor means you and the other co-inventors have equal and separable rights to the invention by default), you don’t have any rights to an invention absent those parties or their assignees granting you rights to the invention. An intellectual property asset like a patent is one of many things that go into the calculus of what a business is worth, but theoretically you could have a contractual arrangement where you receive some royalty from the commercialization of a particular invention yet have no equity or other interest in the business that is commercializing the invention. An invention, or commercialization thereof, can be the basis for the business being formed and operated, but that IP asset and the business entity are separable things. If you have been materially involved in the creation of an invention, or have been offered some compensation for that or other involvement, it would be prudent to contact a local IP attorney to evaluate exactly to what you may be entitled.