When he comes back into the detective’s life, Michael will do whatever he can to try and return to Sherlock the same kind of guidance and support that helped save Michael from falling victim to his dangerous habits.
When Season 6 rolls around, audiences will see Desmond Harrington enter the Elementary-verse as Michael, a former addict who was inspired to turn his life around by, you guessed it, Sherlock.
It’s not directly stated if Harrington is signing on for a full-season run or if he’ll only stick around in the short-term, but TVLine states he’ll be an “ongoing line of support,” so that might be telling.