Passive tank failures are very rare. There is only 1 sensor inside.
Once we find a solution for adding external active tank temp sensor replace rate will go down 60-70% from whom is interested in DIY. Level sensor failures, like OPs, are much rare. But there must be a way to emulate this signal.
Last resort would be to disable the DEF in DDE(VW did it in a corporate level ) or disable the DEF related codes. These solution will come soon as more and more diesels are going out of warranty and there will be a real demand. In the same way as replacing the dreaded N62 coolant transfer pipe was $6-8k years ago and now is offered for under a grand in many places.