Well it can be either, i think most of the time its a loss of drive, modern bikes have better chain guides so it tends to just slip off leaving you wondering if the clutch has been pulled in, occasionally the chain can bunch up and smash the chain housing but i havent heard of this happening on an F800GS or on any bike less than 10 years old?.( I'm sure someone will correct me here)
how a chain breaks
Here is how i see it
1.The chain will only break if its under load
2.its only under load on the top run
3.therefore it will only break on the top run?
here's the bit that will decide how it pans out
If it breaks very near to the front sprocket the "loose" end could pile into the still spinning sprocket, bunch up and jam
If it breaks further back then the loose end will be driven by the rear sprocket and will coil itself down onto the road.
The reason i think most failures are non-catastrophic is this then.
A weak link is subjected to the most force as it exits the rear sprocket, as it lifts off the last tooth it is carrying the full force of the load upon it, of course it carries on taking this force the whole length of the top run but at the start is perhaps the critical point?
If its good enough to last the whole run along the top run it may just go on the next cycle.
M