Man Vetter I feel for you... The splines look to be in good shape, the output side of the gearbox is fine and driveshaft looks to be good but all that red on the friction disc and the input shaft just looks like dry surface rust. That needs to be able to slide freely... I had a pressure plate and clutch housing that was almost that glazed and I was able to resurface it. The friction plate looks like it didn't handle the heat as well so I'd be weary reusing that for fear of future failure but at least it's not oiled up. Those splines and even the diaphragm should show some kind of sign of being lubed at one point with moly but I see no sign of that.
If it were me, I would first try to get them to do the entire job under warranty stating this was a assembly issue. (Assuming this is the original clutch). If they say no, I would have them check the flatness of the clutch parts, resurface the housing and plate, moly up the friction disc the way it should be as well as the contact on the diaphragm, grease the driveshaft and bone out! Let the cluch cool after the technical skills portion of your rides and know what it's limits are now. You at least get the 6 bolts and washers to put it back with the right torque/tension and a new clutch cover. Check to make sure the rod didn't get bent while the disc was stuck too.
Again, this is all I can tell from the pics and what you said. If you can afford to get the new stuff, it won't hurt! I feel your a victim in this one, you may have had to ride the cluch and heated it up but that doesn't change the fact that there was no lube on the splines to keep,it from binding.
BMW, if that's red moly on the splines, my apologies...
Good luck Vetter
Don't sweat the petty things, pet the sweaty things...