Indispensible for the lovely QGH!
VDFs are a bit tricky without it too! Are there any left??
To give a slightly more serious answer.....life moves on. If you're working in a known traffic environment with solid and reliable SSR, maybe even mode S, perhaps we can live without DF these days. Change the environment to that UK speciality of providing a service in a mix of class D and class E or G and i would say it's still a vital piece of kit to help to maintain situational awareness.
Theoretically, in Europe anyway, any unit that is removing a DF installation from its armoury will have to do a risk assessment and, if necessary, take mitigation measures on the change. I guess this should be available so you can see how much the DF contributes to the safety of the service and what is being done to mitigate any hazard resulting from its removal.
