Failed rootcanal from 10 yrs ago - extremely decayed, broken to gumline. located top, back molar. will i need to have my gums cut for extraction?

Treatment plan: Have your dentist discuss a treatment plan period. The dentist or oral surgeon will remove your tooth, but how do you want to replace the tooth? Discuss all options with your dentist.

Possibly: It depends if the tooth fractures or not during the procedure. Why not ask the surgeon who is going to extract the tooth ?

Surgical Extraction: Removing the fractured and decayed tooth may or may not require reflecting the gum tissue. First, we don't always know this in advance. What appears as a simple extraction can become more complicated and what would seem like a difficult surgical extraction often is simple. Also, cutting the gums often allows the surgeon to remove the tooth with less trauma and therefore less pain and swelling.

Decayed tooth: Cannot answer without examining you. You will get best answer from a specialist Oral Surgeon who is best trained and skilled at performing difficult extractions. Sounds like it's not the root canal that failed as you are describing decay of the crown of the tooth, not the roots.