I'm trying to think of different ways that this scenario can play out. If anything can go wrong, it will from time to time. My comments below are not meant to be attacks. Please don't take them that way. They are just more things to think about if this ever happens to any of us.
A fanny pack is not a purse with a long dangling strap that can easily be cut and carried off.
Pickpockets all over the world steal them by slashing the strap with razors/boxcutters every day. If a pickpocket can do it in a stealthy manner, then someone who is willing to knock you off of a bicycle to rob you is probably not going to be worried about being gentle with that blade. Knocking you off of the bike is a tactical move that carries with it the intentions of disabling you, at least to a degree.
The only way someone could cut off my fanny pack without cutting my flesh as well...
Exactly. I don't want to give the bad guy the benefit of the doubt. What if the bad guy doesn't care if he cuts you in the process of trying to take the fanny pack. Maybe, if it's tight, he won't be able to effectivly cut it free, but he may cut you up badly while he is trying to get it. Yes, if he is that close to you, you might have the opportunity to fight back, but if he happens to have a box cutter in his hand at that range, you may still end up looking like Swiss cheese after you get done showing him all of your moves.
Besides, how did they get that close to me without my taking action? If its that blind a corner they could conceivable pull me off of my bike, but while they are doing that I can disable them.
Anything is possible. Just because you cannot see them doesn't mean that they cannot see you. The element of surprise has been used to take down many prepared men. As much as we might prepare and train (which is good to do), there is always the fact that sometimes things happen that we just do not see coming.
this type of attack can be overcome.
Sometimes. And sometimes you end up looking like Swiss cheese.
What defensive moves work best from a bicycle? Can they remove you with one hand or will they need both? How does that affect your options? Just thinking through the situations will give us a big advantage when and if the time ever comes for real.
Good questions. How many hands? No one can guess how the BG would do it. My first thoughts would be that he would use two hands. What about inertia and momentum? Would they work for us or against us? I don't know. If I were yanked from a moving bike, I imagine that my balance would be lost for a couple of seconds (or more), I may be stunned or even injured from crashing to the ground. How well could I fight with a broken wrist or ankle? Could I manage to get my gun with my weak hand if my wrist is broken on my strong hand side, while I am having to fight him off with the broken wrist side? I hope that I don't have to find out.
Nothing is set in stone when it comes to any scenario. There are just too many things that could go differently each time that they are played out. What if you land on the back of your head, breaking your neck? What if you land on your feet? What if the BG loses his balance and falls on you, accidentally shoving his blade into your gut as he falls? What if he pulls at your pack, accidentally pulling it open (exposing the gun). Will he get the gun? Will he use it? What if... Many different things could happen that might give you the upper hand, or many things can happen that might give him the upper hand. Anything can go wrong... or go right. Just some thoughts.