EDIT: I re-read and you mean the pedal! not the crank, sorry for the confusion...
The pedal is probably ruined, and I doubt you can re-use it, a damaged thread is unrecoverable, but depending on the pedal, you can unscrue parts of it to salvage.
Below is my mistaken answer about removing a crank:
This happened to me recently, and my solution was to hammer the crank (knowing that it will become useless, — it was anyway, since the threads were destroyed).
The way I did it was to place the crank (the part that connects to the bottom bracket) on top of a vice and then hammer it hard (I mean hard, a soft blow won't work). Hammer as much as you can until it gets out. The main problem with this method is that it may ruin the bottom bracket.
The objective is to deform the crank so that it comes out.
From my experience, a metal crank is harder to remove, whereas an aluminum one is easier.
Also, (I can't really tell from the image you posted) if the crack has a plastic surrounding it, remove it, because hammering with the plastic cover won't have the same effect as without it!
On one of my attempts, I sawed the crank hoping to make it fragile enough for it to come out, but trust me, it doesn't really work and this will most definitely ruin the bottom bracket...
Finally, and if none of the previous worked, you can remove the bottom bracket (BB) from the frame (depending on the BB type, the old ones can be removed), you can use a pipe wide enough to fit around the BB, and hammer the pipe so it loosens the crank. This one is the toughest method and I've one crank that will be subjected to this method when I return from my holidays.