Quite often there's an indication of a problem before a part fails. Usually when brakes fail on a car they were giving the driver warning for a long time but the issue wasn't addressed.

I can't recall seeing it but was there any indication that you were having a problem with the engine? Were you experiencing less power than 6 months ago? Was the engine acting up before you went out the day the engine quit? With a blocked riser like that I would think that before it blocked completely it would have become restricted causing a change in your engines performance.

Did you notice that and pretend it didn't exist or was the engine running great and on the day you went out the problems appeared.