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Welcome to Just Answer. Are the wiskers falling out completely? Are they breaking off with shorter pieces remaining attached to the skin?
Is he grooming himself more? Any other hair loss on his body? Any weight loss or other issues with him?
If the hairs are breaking off, I too would be most suspicious of trauma to them. Him biting them could be part of the problem. Could he be breaking them off on something else in the environment too? Also possible. At this point, there are some rare situations where the hairs can become brittle and break, but this doesn't sound like it. As far as needing them to navigate, they do provide information when walking in the dark, but most of the time they are not absolutley needed to get around. Honestly, I would watch him for any other hair loss or other issues in relation.