Selling vehicles with shared orders does not crash the game.
NOT_REACHED triggered at line 1719 of ..\src\vehicle_gui.cpp
Steps to reproduce
This is a tricky one to reproduce.
In the attached savegame autosave14 (not the emergency save), open the New Mills Airport station (just north of the starting location in the savegame) and look at the list of trains with that station in its orders.
Group the list by shared orders
Train 289 is in the list, currently lost and near a depot. Click on it and send it to the depot
In the depot, drag the last vehicle (an EMU) off the train onto a new line