How long may it take for a dental gum fistula tract to be less sensitive in that gum area if the canal root retreatment is successful?

Fistula: You had a draining fistula and this area will take some time to,heal after the root canal is completed. The pain should be decreasing but it may linger for a week or two. If it is not healing and decreasing then follow up with the dentist who did your root canal.

Varies: But a few days to a few weeks would be normal. Everyone heals at a different pace.