Customer (name blocked for privacy),
You are right. There is not an oil pan on this model. There is however oil lines. It is possible that one of these have been punctured. A seal? Hopefully...
It would take a great force to crack the crank case with a rock. Great enough to throw you off of the bike.
If it is the case. It may be possible to weld or reconstruct although it is not recommended due to the likeliness of it coming apart, oil soaking the rear tire and causing an accident. The cases are sold together as a unit because of the precision cut to make halves.
If the initial question asked has been answered, please select the "ACCEPT" option and Thank You very much for your question!
Here for you,
Glenn II