Need Help with Drain Pipe

I can sure use some advice on a problem I have with a drain pipe. A rough sketch is shown below. At a point where the cast iron pipe joins the "T" it's partially rusted through. I would like to replace it, but the pipe will probably break at the rusted point leaving the threaded portion inside the "T". Any advice on what is the best way to resolve this problem will be appreciated.

Cut off the old pipe and unscrew it, if any thread stays in the hub, peel it out and re-tap it, then use a pvc male adapter and go from there.