So, further to the story of the cancelled Merredin Link...
Turns out the Avon Link (which uses the same set) didn't depart Midland last night (apparently due to a defective engine cooling system). That meant that this morning's Avon Link didn't run, meaning that the Merredin Link couldn't and tonight's Avon Link won't either.
Also, one of the two Prospector sets is defective (blown traction engine), meaning that at least one Prospector service is cancelled every day until they fix it.
Additionally, the Australind service to Bunbury has been suspended since last year due to major track work. The rolling stock that was retired when the Australind was suspended has not yet been replaced.
So, today, only one of six planned long distance trains is running in Western Australia, there is only one serviceable diesel railcar set in the state.