Sometimes it is possible to make the fireplace appear more symmetrical as shown in the mockup below. We use a bifold fireplace door with black glass that you cannot see through when closed. The doors on the right would open to the fireplace and the ones on the left would have a black steel plate to cover the stone. Paint the inside of the fireplace black and it's not too bad when the doors are open, but you cannot tell the fireplace is off-center when closed. If you are intrigued by this concept, post these measurements and I'll do some calculations to see if it can work. Measure the width and height of the fireplace opening and then how much stone there is on the left and right sides of the opening. Don't measure the current door frame, but the actual fireplace opening itself.

I would sure like to know what is under all that paint and stuff. Could be some nice brick? If not then my thought is something right to the ceiling but no mantel.

A hearth may be required (depends on local code and type of insert), but a full wall of stone is not, so they should be able to do something simpler with the space -- however, if they do, they will probably need new flooring in the room, so that's something to take into account. I wouldn't aim for the TV over the fireplace, but a smaller surround will probably mean that the TV can move closer, making it easier to arrange furniture to enjoy both. And have art hanging over the firebox too! Honestly, once the stone comes down, the world is your oyster, so you just need to look at some photos and get a sense of what appeals and fits with the character of the house and your parents' stylistic preferences.

Here's a couple ideas. There are so many choices of materials to choose from, but you can take it all the way to the ceiling. How high is the ceiling? Can you step back far enough to take a picture of the fireplace wall floor to ceiling?