Honestly I think BMW is being more than fair. There is a clearly defined and long standing line in the sand, and you're on the wrong side of that line- 3 days, 3 weeks, 3 months, 3 years... doesn't matter. Does it kinda suck that you missed it by just a bit? Yep, but as they say, that's life
The 50% which has been offered- is that towards the full repair cost- parts, labor etc? Or only towards parts? What is the anticipated final cost to you?
I'm curious since, while I respect your desire to remain stock, replacing like for like will eventually result in the same problem- the new ones may last a year, or may last 8 years & three months... It's a crap shoot. However, there are some nice aftermarket stock equivalent replacements which resolve the known issues and would be a better long term replacement than a fresh pair of stock turbos.
Of course, if you're just going to sell in in a year-ish, I suppose it probably won't matter to you, it'll be a problem for the next owner to worry about...