If you can, take the rifle out somewhere and shoot the charge out of the barrel, that would be a good start. It will not do more damage to the rifle at this point. If shooting off the charge is not possible, at this stage, I would kill the charge. Pour some oil down the muzzle of the rifle and let is soak into the powder charge and around the projectile. This will come in handy for a number of reasons. It will kill the powder charge, it will lube the projectile and it might help in freeing the breech plug. After the charge is killed, the first thing you do is remove the breech plug and push the projectile and charge out. After that you really need to get the breech plug out and examine the threads of it for damage. If the breech plug threads are damaged, get a new one. And then see what kind of barrel damage is in there. Once you get a look in there it would be easier to decide what steps need to be taken to see if the rifle can be saved.