While the complete tear down of the dash AND its framing is a bit extreme, it is, in principle, what needs to be done to access the main blower motor. Bentley's manual does a great job providing a general outline of the procedure to access the blower motor. Also, depending on the year of your X5, removal may be slightly different than described here. This video provides an overview of the broader steps and caveats of the dash and center console removal. The minute details require removal of a significant number of screws, steering wheel, fascia panels, kick panel lighting, wires, airbags, center console, etc.

Be sure to test the function of the new fan motor (if you go this route) on an external battery. Turning your X5 on without airbags connected throws the airbag fault. This can be cleared with an appropriate code reader if you own one; otherwise, you need to take it to a shop. After mounting the fan, spin it by hand to make sure the fins are not rubbing the housing--you only want to disassemble the dash ONCE.

Here's hoping it's the sample fan--i.e, the relatively easier fix.