My high valley stove only has bricks on the bottom not the sides and they are heavy. I have burned some hot fires the last 4 season sons on it and they dont look worn at all. Id say they will last another 5 years easy. My vogelzang has bricks all around the stove on the inside. I think they are the heavy type.
My dad said he never changed a firebrick in all his time burning, that his bricks out lasted his stoves. Times change I guess.
At the rate the ones in the HV are wearing I bet they go another 15 years but not knowing how the time may increase wear I just went with 5 years? But yes they look like they will last forever.