When we have had contactors stuck slightly in before on say West motion on an EOTC, it stops the east motion electrically. Maybe we just use a different brand of contactor.
The only thing with just scopping it in the bin and replacing it with an identical type is that there may be nothing stopping it happening again. I take it your company carried out a full investigation into the dangerous occurance?
It has been fully recorded as a H&S and EAW issue with the customer, my experience of them in the past is that it doesn't usually stop there. There is quite a good mantenance record and the last 'fault visit' to that control system was quite a few years ago so it seems to have been reliable till now. They have already made and fitted warning notices on the DB's. They are not taking it lightly.
Of course no one knows how long its been like it, both supplies are on the same phase...
I to have found countless other incidents of things like photocells not wired properly, borrowed neutral it one thing borrowed live is a whole new ball game.