The piston and cylinder will most likely be scored and the rings will be trashed. Does it have no compression at all or is it just low? The cylinder does comes off of the crank case. I am not sure if they still carry cranks... but they may since it is a newer model. I would assume a whole top end rebuild is in order as well as a thorough cleaning of your entire intake. You will not know the real damage until you tear it apart though. Does the engine even turn over anymore?
I did a complete top end rebuild on my robin 244 2 winters ago with great success. I took pictures along the way as well. They can be found
HERE. My 244 is slightly different since it has an internal starter/alternator but the top end is exactly the same as yours!