Crank Removal of Stripped Extractor Threads
If the removal threads for the crankarm puller in the crankarm are damaged, there is a possible repair. You will need a Bicycle Research TC-8, which is a fluted bolt that cleans the threads. It comes with a pivoting stud to align the tool concentric to the threads. This tool in not a tap, it only aligns damaged and cross-threaded threads. It will not cut new threads. Typically, it will not damage threads, so there is nothing to lose in trying it. The TC-8 will work only with square drive cranks.
If the threads are completely stripped, the is basically ruined. The arms can be typically removed, but it will be unusable. The simplest removal method is to understand how arms keep from falling off. Pressure from the crank bolt keeps it on, so you need to remove that pressure. Loosen the bolt or nut three or four turns. Ride the bike hard, uphill. The crankarm hole is a tapered fit onto a tapered spindle. The flexing will cause the arm to loosen, but it will also cause the crankarm hole to become enlarged, ruining the arm. Use care when riding, you don't want the arm to fall completely off when pedaling.
It is also possible to use a hacksaw to cut into the arm at the spindle joint. A cold chisel can then be used to split the arm.