They never die :-( .
Stop all pumps. Have a nice scissor, one brand new, well washed, that you will only use for your tank. Cut the Kenya tree at the base. Exchange for XX at the LFS.
Always will be a leftover tissue over the rock, doesn't matter if it is big or a very tiny piece.... it will grow back :-( .
If you want to stop it, cover that left over tissue with reef putty. If you want to keep it, prune them from time to time, unless you want to finish with a Kenya tree dominated tank.
Enjoy the life of reefkeeping! !!!!