Michael Fooks wrote:
firstly no one's advocating that the OP only do BJJ, but I think you figured that out.
Secondly if you're on the ground and he's got knife - how would you avoid getting stabbed?
The same way you avoid getting stabbed while standing, attempt to control the knife hand.
I've found that a lot of people open themselves up to wristlocks on in ground fighting. While they wont end the fight, they give you space to move your hips and get to a better position (or escape and stand up if this is the street). I've rolled with small joint manipulation allowed and once I had a new guy attempt to eye gouge me. As long as you can maintain the superior position you are mostly safe from harm. The problem with most bjj guys is they will sit in their guard. This is good for bjj competition, but bad for mma and 'the street'. But if you can maintain a superior position then you are safe from your attacker, and most likely can stand up and escape.
The biggest thing to remember is to move off the line, learn how to sprawl just in case, and control the head of your attacker. If you can keep that in mind you and you go to the ground you have a good chance of being the one in the superior position, which will let you get where you want to be faster.