A few bruises, that's all!
I purposely bought mine as a non-ABS model, to avoid any potential issues. Only the very late STs got 'normal' ABS - that's the system that, should the ABS fail (warning light on instrument panel) you still have full braking, just no antilock facility. The earlier STs (most of them, I think) had the servo-ABS, often referred to as 'whizzy' brakes - that's because, when you turn the ignition on, you can hear a 'whizzing' sound for a second or two as the servo fires up. If
that system fails, you're left with what BMW call 'residual' braking....apparently, around 20% of the norm - people who've experienced it refer to it as being '****ing scary'!

Without the servo, the brake lever needs a much, much bigger amount of 'pull' to stop the bike. So....most people, when faced with the £1500+ bill to sort the system, have it removed - quite a few of the well-known indies do it (RGM, Overland and Classic etc) at prices from around £200 up to £400. You're then left with a standard, non-ABS system just like how some of the bikes came out of the factory - no warning lights, no other electrical glitches at all.
My current RT has servo-ABS, I'll be having it removed when (not if....) it fails! I don't really like it anyway - the brakes feel very grabby, especially at low speed. They are
very powerful though, they really do pull the bike up quickly the odd time I've needed to, very reassuring....but I know, deep down, that the servo
will fail as I'm going downhill, at speed, fully loaded...just as the lights at the bottom change to red!!
Another plus for no ABS is the ease of home servicing, if you do your own - it's a piece of cake to change the fluid, it's much more complex on ABS bikes.
Pete