I agree with Pum above. Mine was a Stage 0-1 ... and even that is a Melanoma dx for which every Melanoma dx is serious ... but the higher your level, the potential for more treatment is probably indicated, etc. So glad to hear the margins are clear. What is his next course of treatment, if any? Please let us know and keep in touch. Good body checks every month is imperative for your husband, as well as your Dr will want to see him at least every 6mos for followup checks.
C~
You need to ask that question of your specialist but the short answer is that yes melanoma is serious. I had a quick search on your husband's numbers and they look very positive.
I'm very sorry to read of his diagnosis and wish you both all the best for the future.
Take care.