How long can it take for a damaged meniscus to heal?

It varies. This depends on the extent of the tear and the type of treatment chosen. If not treated surgically, most meniscus tears never truly heal, although with time and perhaps medications, therapy and/or injections sometimes symptoms can subside in 6-12 weeks. If arthroscopic partial excision is undergone, "healing" can take 3-6 weeks. If arthroscopic repair is undergone, healing can take 3-6 months.
They dont. We smooth them with arthroscope they dont healb on their own.
Usually doesn't. A torn meniscus usually does not heal, and requires arthroscopic surgery, to trim out the torn portion.