No, an incompetent primary beneficiary does not have to share the life insurance proceeds with the contingent beneficiary. A guardian of the estate will likely need to be appointed for the incompetent primary beneficiary. Good luck.
The foregoing is a general answer based upon limited information, should not be construed as legal advise, and does not create an attorney-client relationship. It is the opinion of the writer alone.
DISCLAIMER: David J. McCormick is licensed to practice law in the State of Wisconsin and this answer is being provided for informational purposes only because the laws of your jurisdiction may differ. This answer based on general legal principles and is not intended for the purpose of providing specific legal advice or opinions. Under no circumstances does this answer constitute the establishment of an attorney-client relationship.