Def is injected to help with regens into the cat so if the dpf comes off the urea is useless
DEF is injected to clean up the NOX emissions. It has nothing to do with the DPF. The DPF is just for particulates. The DEF has nothing to do with regens. Tons of off road equipment out there with just SCR/DEF and no DPF.
Personally between our truck and all of our off road equipment that is now running DEF, it hasn't been an issue for us. Keeping the warranty intact on everything has been nice. Our LML has nearly 90k on it now and other than the DEF recall it has not had any issues. Out of all of our off road equipment with DEF we have only had issues with one tractor that was a very early model. It had issues witht he sending units but they no longer use them anymore.
We have a nice DEF setup for dispensing it which makes it basically hassle free and at $1.80/gallon its not a huge expense at the end of the year.
Now DPF's on the other hand do make me angry.