Co-inventorship with university inventor

You have all the patent rights that Steve described unless there is an agreement between you and the university to the contrary. If there is such an agreement (and assuming that the inventor had indeed assigned his rights) it will remain in force after the inventor leaves.

If you are co-owners of a patent, I presume that the inventor assigned his rights to the invention to both your company and the university. Co-assignees of a patent are free to work the patent as they see fit - you can sell your share of the patent, you can license the patented technology to anyone, and the like. As a co-owner, you do not need a license from the university. I would ensure that the inventor actually assigned the rights to the invention to both you and the university and that the assignment has been recorded at the USPTO.

You have heard the note about asssume? Make an ass-u-me? When you say 'co-own', could you be more specific? If you have an agreement with the uni, and the inventor was under obligation to assign his/her IP to the univ, no need for the question about what the inventor does. But I fear your ownership is not that clear?