The answer depends primarily on two factors:
1) Do you have outside investors?
2) Do you have and/or could you obtain a legal release from the co-founder, and after this release, would the co-founder have less than 5% of the company?

If you have outside investors in the existing corp and you wish to pursue the pivot, I would strongly encourage you to continue within the same corp, unless you didn't properly organize your co-founder agreement, in which case, your co-founder has "dead equity" which makes further funding much more difficult.

This advice is not being provided based on a legal expertise but rather a practical perspective as both an entrepreneur and investor in early-stage companies. Happy to provide more specific advice if I understand the context better.