Connecting PVC to Galv Pipe fitting for Drain
Which ever solution you chose, removing the threaded galvanized pipe should not be a problem.
Cut the galvanized pipe within 3/4" from where the threads start. Using a chisel, cave in the pipe just above the fitting, then the end of the pipe will easily un-thread from fitting using channel locks (water pump pliars). Using this method will leave the threads of the fitting intact and surrounding pipe will not be broken, damaged or moved.
btw, this is similar to removing a brass plug from cast iron hub (i.e. cleanout). Cut, drill or chisel out the inside of the brass plug, then cave in the plug just as it enters cat iron fitting.
I hope this helps.