I do use a sealant now, but your LBS is right, it would not have helped that leak one iota, as it was a structural failure.
I avoided sealants in tubulars, for years, but @
ldmataya convinced me it was a good preventive measure. Now I put 2 oz in each new tubular.
Peace of mind issue, perhaps, and of course, subject to change if I flat and get all psycho twisted up on it.