Adblue Fault, no restart 650mi, A4 B9 2.0TDI

Just had this message on my dash on an a4 b9 2.0 tdi. Got it scanned at the garage and they have recommended to get an ‘Ad blue delete’. Can someone please tell me if they have chosen this option before and how is the car now, have you guys had any future problems and most importantly they did mention that it will pass an MOT. I understand it is slightly illegal but how would one get caught?
For info I got quoted £180 for a delete and £3000+ for a replacement.

Any advice is highly appreciated.