That train's delivery station was disabled after pickup, and there's no other station on the map that'll accept its product... so it went back to the waiting bay, clearing the pickup station (and other tracks) for other trains to serve. That's good behavior- but I'm rather surprised it hasn't sent me a "Train cannot deliver <Product>. No valid destination" warning like these trucks will if I turn off their sorting plant (and the global rock-accepting storage):

Can we perhaps get one, so we don't wind up accidentally devoting entire trains to eternal dormancy by not noticing that one was loaded up for that station we just eliminated?

... I actually knew this one was there, since I was only remodeling the entryway, and only paused the station because it was throwing no-route errors and I wanted to clear the tracks. Speaking of, can network trains with no route to destination do as trucks do, flag it as a no-route destination and treat it like it's not there, allowing them to automatically clear the tracks for other trains/duties (whilst also posting a "station unreachable" warning)?