The problem is that most of the GA flight can't move to Mogas or the UL91/96 because the engines won't run on it and there are no alternative engines for them.
My Cessna will not run on low Octane fuel and neither will something like Peters TB20.
So ending Avgas will effectively ground most of the GA fleet and thus end GA. Now the Microlight and Permit boys may just sit there all smug that they can carry on as they have no problems. But with most of the GA fleet gone the world will become a whole lot smaller and without the big GA targets in the way to run interference, how long do you think it will take those with idle hands to target you? Someone has to feed the CAA machine........