If there is no way to 'fish' out the critter then there is really only one thing to do... My neighbor is a well driller and he said to put a gallon of Clorox down the well and run the water til you smell the Clorox at the tap. When you smell Colorox at the tap it means that it is now in your pipes also and can work on killing anything in the lines. Oncce it is in the lines let it set for 24 hours then run the water...should discharge the water away from the area with a hose.
If the first gallon of Clorox doesn't quite do it then hit it again the same way.
He said to stick with Clorox brand directly...and not to use something like muriatic acid, he has seen people try this and ruin their systems and pollute the ground water.
I would probably do the Clorox routine at least three times over a three week period. One other thing he said if you want you can use the chlorine pool pellets and drop a few of them down the well while you are away...and run the water when you get back...this will allow a slow release of chlorine and help the overall process.
...and as you most likely have done, close up the well head with something that can't be chewed through by a varmit.