The rationale for implementing derailments is to have visible consequences for mistakes (speeding, slamming brakes on loosely coupled stock etc.) instead of just abruptly halting the simulation. Basically having the train grind to a halt with appropriate sound effects and clouds of dust, but nothing more spectacular than that. Having a wheelset drop on the ground and bump over sleepers could create an interesting visual feedback in the cab, given the physics modelling of the bogies and driver head.
Thanks for the quick reply!
And yes, it sounds good - Except there won't be much of grinding to a halt in a high-speed derailment, witness accounts of real-life occasions of which had included words like "somersault" - To be fair, that was an occasion of animal strike with traction at rear, rather than any driver error.
A combined approach might bear consideration, at some point.