I had a 92 520i and this happened it was a fuse link in the engine bay. Now i know this will not be available at this time of night so a solid wire link (not normally advisable) to temporary power the windows
This could be the fix but not sure if the same on the e36 but guess its worth a try...
The sunroof has a manuell reserve closing. It should be described in the owners manual. Usually (E34, e28 etc) it can be revealed by removing the sun roof switch panel, there is a "screw" under the lid that can be turned with a wrench etc to close the sunroof. This is a option in case you can`t get power to the electrics (fuse?)
Windows are harder to shut without power, but there could be opening in the doorpanel (a plastic round cap) for a manual closing handle.(Everything here is based on older models, not really sure about E36)
Thanks for all the help again, I opted for the "try and cover sunroof & windows with board and bin liners" option just to try keep the car dry overnight, and today going to drop it in at the garage so hopefully they can sort it.