Crash-proof Laptop bags for MacBook Pro for Bicycle? I'm thinking of getting a new bike, one with a Pannier or Cycle rack; my job requires me to travel with a Macbook Pro and there are several issues.

1). I am worried about crashing/wiping out and breaking the MBP.

Is there a recommended crash-proof bag, or a bag that securely fastens it so that it does not bang against either the side of the pannier; or when you put the bag on the floor it doesn't hit the laptop?

I've been looking at the Hardcase shell and the bags you can get for MBP at a local Apple store; however they look flimsy as hell and only appear to be there to reduce scratches.

a) Are hardcase shells (as sold in the Apple stores) designed to withstand this kind of damage?

2). The additional weight will make the bike sway around corners, when braking, or when climbing up hills.

This is a particular problem that I am unsure how to solve.  I could carry the laptop on my back, but ideally I want to move the weight from my shoulders to the pannier.

Another possible solution would be to put a counterweight in the opposite bag, but this means carrying much more weight than I need to; additionally I do not have anything to act as a counterweight. 

Another possible solution is to put it on the central (top) pannier rack behind the seat and use straps, etc to securely fasten the laptop bag.

The problem with this is rain, especially if its sitting flat, it'll just collect moisture, and soak through.

I am based in the UK.
I have never seen anything that would do this. I've done a lot of looking over the years because I carry camera gear as well as laptops, and neither like the hammering they get when attached to the bike. My solution is insurance.

Broadly, the problem comes down to suspension. On your back the load gets the benefit of your soft, flexible body and your tendency to lift off the seat before you hit big bumps. That last is key - whatever suspension your pannier offers has to be able to cope with a nice hard thud as you bounce off a kerb or through a pothole.

What I've seen used is the Ortleib backpack, which is nicely waterproof and can use the padded laptop sack that goes inside it. You could use that sack as intended in a pannier on your rack, but even with a solid state drive I expect your laptop to fail within 5Mm if it's in the pannier. On your back it shouldn't be affected. Likewise, a decent courier bag (Ortleib again, Crumpler or other)

What I actually use is a standard pannier with a home-made foam inner to pad the laptop. That gives more padding than anything I've seen commercially available, and it's cheap. Find a shop that sells slabs of foam, buy one the size of your pannier, cut a slot in it to take your laptop. If you buy two panniers inevitably the second one will fill up with stuff, balancing the load. Trust me on this :) Mine has my wallet, puncture kits and multitool, lunch, rain jacket, phone charger, I dunno, suffice to say that it weighs at least as much as a laptop does. And I only carry the one pannier and the offset weight isn't an issue.

A hardcase sheel that will withsand a crash is going to weigh a lot. There's some discussion in this answer: Secure Storage for Running Errands and in this question: Ever seen a locking bag that could be locked to the bike?