You can drop the older GSes pretty hard with nearly no consequences (other than bent mirrors, broken indicators and possibly bent bars). Dropping the bike without crash bars on rocks can be unfortunate (think gaping holes in cylinder heads).
But if you are going to do 90% off-road, I'd have to agree with laughing Bob: get something smaller. Either a KTM LC4 or a GS 650, or possibly a KLR 650. That should do you just fine. If you must go for something bigger, then consider a KTM 950 (heresy to say that around here, I know), as it's lighter than either the 1150 or 1200, and more off-road focused.
David