As much as the DPF system is a complete pain, it's unusual and even unlikely for one to 'fail'. There are no moving parts involved, it's just an exhaust section with a few internal baffles with holes in them...a cyclonic injector that scoots in the DEF (Adblue) at one end and a temperature probe at the other. A bit of an over simplification... but that's basically what it is.
The common cause of a DPF system recording a fault or failure is for the injector to be completely clogged with crystalised urea (synthetic pig pee) from the DEF solution in combination with the main baffle plates being sooted up and full of ash which stops the DPF system working to the point where even a forced regen won't solve the issue. Hence the 'fail'.
I'm surprised that LR Assistance didn't at least attempt a forced regen, it
may have helped by temporarily solving the problem rather than just clearing the fault codes, telling you it's broken and leaving you to get on with it.
Although it's extremely rare, I have seen the temp probe failing or being broken off...but that can be individually replaced for a fraction of the cost of replacing the entire DPF unit.
Having the DPF system cleaned professionally or tackling the job on your own with a 5L bottle of Wynn's DPF cleaner will usually solve the problem. I'd suggest cleaning out the throttle body and check the operation of the butterfly valve at the same time should you go down the DIY route....a sooted up throttle body or a sticking butterfly valve can be a contributing factor (amongst others) with repeating DPF faults.
The DPF system can be cleaned in situ without removing it, which is how small indies (and me at home) or mobile DPF cleaning services do it...but that requires a pressurised bottle fitted with a rubber tube to inject the cleaning fluid via the DEF inlet pipe on the unit...which is by far a lot easier than removing the entire DPF unit. Although not
quite as effective as removing the DPF and soaking it in Wynn's for 10 hours...it works.
One of the first bits of preventative maintenance I did on my '17 HSE after I bought it was to clean the DPF...since cleaning or servicing the DPF system isn't included as part of LR's normal servicing schedules, the chances are it had never been looked at since it was fitted in the factory.
'Servicing' of the DPF isn't normally required since the DPF system 'self cleans' or regens as part of it's normal operation. The DPF unit does build up ash and soot on the baffles over time though so an occasional clean will help alleviate this.
A lot of stop-start or short distance town driving doesn't help as the DPF has to get up to temperature to work properly... Once a month, blast it up the motorway or get the engine up to 3k RPM between gear changes to get that second turbo kicking in once it's up to temperature will help a bit. So...if your main driving is at low revs around the town...get it out of the garage, get the boy racer shades on, flick the gear selector into sport mode and thrash it every now and then
It's not a particulary difficult job removing the DPF unit except for requiring a bit of heat to unscrew the temp probe...the only
necessity being after cleaning the DPF... either off the car or on it... you have to tell the car's ECU via an IID tool or similar ODB diagnostic tool that the DPF unit has been
replaced. Just clearing the fault codes with a diagnostic tool after cleaning will do absolutely nothing except put the warning indicator on the dashboard off for a while.
Chances are that many of the smaller Indy garages or local services that offer DPF cleaning may not have an IID tool or diagnostic software for Land Rovers. It's an issue to be aware of and should be enquired about at point of contact should you decide to try having the DPF cleaned. The 'on the car' cleaning process takes upwards of an hour roughly if done properly and costs vary...shouldn't be more than £200 typically....but I'm going back a while.
In the unlikely case that you can have the DPF unit replaced under warranty...go for it by all means, but in the end...I'm quite sure that Land Rover will be perfectly happy to relieve you of 3 grand to replace your dirty DPF for a shiny new one
A couple of links for specialist Land Rover DPF cleaning services:
https://www.ukdpfcleaning.co.uk/services/land-rover-dpf-cleaning/
https://dpfexperts.co.uk/mobile-dpf-cleani...-cleaning/