Ok this is on C7.5 but folks have reported the same on C8.5 as well.
My C7.5 crashes on exit EVERY SINGLE TIME. Turns out the problem was having loopMIDI virtual midi driver (for lemur to function I need this). When I exit loopMIDI and try opening and closing Cubase it closes with no issues! Tried it several times with and without loopMIDI and I get consistent behavior everytime (crash vs. no crash).
So - check your MIDI driver - see if you have old MIDI devices, or virtual MIDI ports like me in your setup. Not that Steiny is going to provide a fix for it, but at least you know who the boogeyman is. Hope that helps!