a game with Narrow Gauge crashes when loading if narrow gauge missing
screenshot load a pak64.german game on pak64
There isn't really much else to do about it. Loading the game without this will probably not make any sense, as major parts will be missing. Sure, Simutrans could keep running, so that you can load another game instead, but the amount of effort required for this outweighs the gains from fixing such a rare problem in my opinion.
I assume automatically deleting such narrow gauge objects if no data is available for them is out of the question?
Well, some objects are not really linked directly to narrowgauge, like the stations or bridges and tunnels.
Before SImutrans failed much more often when industries were missing. But as said, it does not make sense to load such a game if large areas of stuff is missing.