Yeah, it's uncommon across sports but I think there's a scenario where he gets another one in before the significant drop off in play, which will happen at some point. He has four years after this one so they could theoretically take care of him again half way through that term if they're still good.
The Avs are in a very similar position with Bednar as the Bolts are with Cooper. Very similar style coaches, on teams with long windows of contention, with GM's that don't make panic moves, and respect their coach a lot.
Cooper had 9 seasons with Tampa and got a 3 year extension. Not sure when his previous deal expired.
Bedsy has 7 season with one remaining and got a similar 3 year extension.
I can definitely see him being re-signed unless the Avs unexpectedly miss the playoffs and have a bottom dweller year at some point. Even still I bet Joe and CMac give him another year to see if he rebounds. If they didn't fire him as a rookie after a 48 point season, they're not gonna fire him after one down year with one or more Cups and President's trophies under his belt.
I actually wouldn't be that surprised if Bednar and Cooper end up getting let go in the same year eventually and swap teams. They'd fit in seamlessly on each other's teams with their GM's philosophies and team makeup.