Katras can be returned to the body. Such was the case with Spock, who, near the end of Star Trek II: The Wrath of Khan, implanted his katra into the mind of Dr. McCoy before sacrificing his life. In Star Trek III: The Search for Spock, a mind meld ritual, the "fal tor pan" ("re-fusion"), removed the katra from McCoy and implanted it into Spock's regenerated body. The ritual was successful, though it carried risks for both.
Katras can be re,turned to the body. Such was the case with Spock, who, near the end of Star Trek II: The Wrath of Khan implanted his katra into the mind of Dr. McCoy before sacrificing his life. In Star Trek III: The Search for Spock, a mind meld ritual, the "fal tor pan" ("re-fusion"), removed the katra from McCoy and implanted it into Spock's regenerated body. The ritual was successful, though it carried risks for both.