This is probably too late to help you, but perhaps for the next one in trouble. My window was also all the way up. Luckily, that also meant that I could access the bolt that holds the window through the access port which is there for easy access to the top bolt/screw of the window regulator frame itself. I removed the trim, sound deadening material and loosened the side weather strip, which allowed me to manually lower the window safely.
Since this was brought back up, I'll use the opportunity to ask those that might be familiar with the lift mechanism. This week my son lowered the passenger rear window and now it will only raise about an inch and a half above the sill. It seems to go all the way down. I'm going to assume that something is getting in a bind on the way up and stopping the motor? I've pulled on the window as it comes up to help it, but no go. Has anyone experienced this failure mode. Thought I'd ask before I remove the panel and vapor barrier (after I finally got it sealed:crying).
That process is one of the early signs you are going to have to replace the regulator. My personal experience (six regulators in 15 years, three BMWs) is that the top pulley, circular guide whatchamacallit, develops cracks which bends. misaligns the cable, and then you get intermittent, sometimes works, sometimes works somewhat, but it will fail soon-ish.
This year is the first time I tried non-OEM. One of the ones seemed to be near OEM quality, made in Taiwan. Wasn't too worried about that one. The one I bought off of EBay, with a five year warranty, was vastly inferior materials. I might change my mind, but I'm pretty sure I will go back to OEM... especially if this aftermarket ones fail quickly. My 2001 M5 only has had two go bad, both this year. A 1998 E38 had three of four go bad, seemingly about every six months for short time.
Hope this helps prepare your outlook, you might get lucky though.
It looks like the failure in mine was the red plastic part where the flex tube connects to the frame. The tube wrapped around the pulley, the cable got all bound up in the spool and it was generally a mess. I am pretty sure I could have rebuilt it by remaking parts from aluminum rather than plastic, but it was in pretty sad shape overall and the motor brushes were getting short. My time is becoming more valuable now that the kids are older so I just ordered an aftermarket one from Amazon for $150. Looks very much like the one that came out of the car. Just haven't had time to get it mounted yet. My understanding is that these window lifts are the bane of these cars existence, but I'd been lucky up till now.