From Skin and Haircoat Problems in Dogs, Lowell Ackerman DVD DACVD, ISBN 0-931866-65-0
In any case, as long as there isn't evidence of metastasis (spread to other organs, like lymph nodes, liver, spleen, lungs, bone, etc.), I'm not sure why your vet would make a recommendation to euthanize your dog.
Has your dog had multiple, separate nodules removed? If so, have they all been sent for path exam and histologically confirmed as pilomatrixomas? Bassets are also prone to the formation of "sebaceous" (epidermal inclusion/keratinous) cysts, which are benign and which can be numerous. Is it possible that perhaps your dog has had both types of nodules?
In any case, as long as there isn't evidence of metastasis (spread to other organs, like lymph nodes, liver, spleen, lungs, bone, etc.), I'm not sure why your vet would make a recommendation to euthanize your dog.