mirabelleswalker As long as the images you get are fine there isn't anything to be concerned about.
The mirror is not an integral part of the actual image creation. The mirror's function is to let light into the camera body and up to a viewing screen so you can see how your image is composed. Then when you hit the shutter button the mirror flips up out of the way so the light goes from the lens to the sensor.
You can take your lens off and see the mirror. If it is badly cracked you will be able to see it. My mirror has a chip out of the corner. Had had it for years. No problems.
Any internal damage that matters is going to keep your camera/lens from working properly or show up in the image such as lines or blank spots. To determine if any suspected problem is the body or the lens change out lenses (borrow one if you need to) and see if the problem persists. Damage to a body will keep any lens from working correctly on the camera. Damage to a lens means the camera will work with another lens on it.