What Steve says is correct - you did something that's always very risky.
However, I think the follower may be too large to drop down into the engine (fingers crossed), so it could still be (with luck) just lying right there in the top area.
If the follower (tappet) has fallen down into the engine, you're screwed - you'll have to pull the engine and tear it down. Pull the front tappet cover off and see if you can retrieve the tappet before you do anything - leave the bike on the centerstand and do not tilt the engine, or that tappet could fall down "the hole". A flexible magnet might help here - the front cam chain "roller" might just stop the tappet from falling all the way down into the crankcase.
With luck, you can follow Steve's outline and recover. It's very unlikely that you'll be able to get that bearing/tach cover back in place without somehow getting some slack in the cam chain. Remove the tensioner first to get what slack is available, though it still may not be enough, and you may still lose your cam timing.
turn the crankshaft or cams until you're dead sure that the valves are all safely closed and the cam chain has been broken. Those valves get bent in a heartbeat. If either of the exhaust valves were open when you did this, you're probably screwed, you'll never get enough slack to put the bearing back on.
On a customer's bike (or my own), I would never attempt this - but it is your bike, so it's up to you.....
Good luck, Mr. Phelps - if you're captured, HondaTwins will deny all knowledge of you....