Strangely enough, the car felt reasonably tight and responsive. And, while I heard creaks over strange inclines (any time the chassis would flex), it was only recently that there was anything obvious (audibly anyway).
As for work on the car, RRT has done all mechanical work on the vehicle for the past 3 or 4 years and every time I've had it in for work, I've asked them to look at the subframe. The vehicle was in their shop towards the end of last year for some light touch up work and, at that point in time, they told me the subframe looked absolutely perfect with no visible cracks. Now this leads me to one of two possibilities :
1. RRT was checking and there was no visible damage.. perhaps the subframe was weaking from the inside out and it lead to a sudden catastrophic failure in the thousand or so miles the car has been driven since late last year.
2. RRT failed to inspect the subframe (or failed to do it thoroughly enough) and, in turn, did not notice the damage that was brewing.
I unfortunately have no recourse for the latter as it would effectively be my word against that of the shop... I'll take their word at face value as they've never given me a reason to question such (especially James the owner)... but this is a hefty bill for sure.
I'm going to try and check with BMW NA to see if they can help out with the costs (of which RRT is already willing to help me thankfully).
In the final days leading up to the discovery though, I did notice a popping noise whenever I would decelerate. For example, if put into first and given gas, the car sounded normal.. but as soon as I would let off the gas, I would hear a rubber popping sound as if you were slapping two plastic/rubber tubs together...
