Hi - lots of Japanese bikes just come with a 'token' sumpguard - usually a couple of little tubes - nothing that offers proper protection. Personally, I always fit a decent sumpguard/engine guard if im going to be riding on stony unpaved roads or offroad. Usually, when I take the guard off at the end of a trip I'm amazed at how many dings and dents it has in it.
IMHO, if you are going on a trip where the reliability of your bike is important (so, almost any) then it really isn't worth the risk of a cracked crankcase. There are lots of ways of bashing your engine off things (I've personally tried many of them :-)) - even something as simple as clipping a big rock acting as a road marker.
There are lots of makes on the market. Personally, I've always found CRD stuff to be quite good. I've also just bought a SW-Motech one for my KTM (with tool boxes) - the Alu is 5mm thick - it's an absolute beast!
Good luck with your ride!
(04 KTM 640 Adv 'Naartjie'/11 KTM 990 Adv 'Tsumeb')