I recently had the timing belt on my 05 wrx with 78k miles changed and a few weeks later driving about 25 miles per day one of the pullys broke... I was at either idol rmp or 2500 at the most because I was still letting things War up when it happened and I was at a stop when I noticed the car wasn't running any longer. I did try to restart it... Two questions... Could this have happened because of a bad timing belt change and what parts should I be looking at replacing?
Couldn't tell you. You can't over tighten it it has a tensioner that presets the load. if you didn't request the water pump and pulleys to be replaced they probably weren't and that could be the issue. However that's not on the shop.
Yes, the engine could require a rebuild. On an interference engine there is the likely hood that a valve could impact the piston. Best case scenario it failed where nothing hits. Mid case scenario it hits a valve and bends it and only the heads need rebuilt. Worst case scenario valve hits piston damages the piston, breaks off damaging the head and cylinder walls.