Could well be wrong and at this stage can only really be theoretical.
200, 300, older TD5, 130, tipper, Hi-Cap, mewp and all the other weird and wonderful creations will be fairly safe price wise. They have hit the bottom on their pricing, a 200/300 can be picked up for decent money and is a good dog car, weekend toy, off roader etc and can be beaten about, spanner it yourself easily, stand on its wings without much thought, wash it out and life is good.
However, you start getting into the 2010-2015 Defenders. XS, County station wagons and the like that are commanding 25-50K they are no longer any of the above, apart from a shock absorber and other basic mechanics, you aren't going to do much work on a 2.2 TDCI with DPF yourself, you don't really want to chuck dogs in one and stand on the wings with stone filled wellies when you own a 35k late Defender. They are uncomfortable to drive, anything over a few hours and you struggle to walk after, rubbish heaters, window needs to be open to steer it any sense etc etc. (Don't get me wrong, I love a late TDCI Defender)
Now you will be able to buy a brand new Defender with manufactures warranty, all the mod cons, spec for spec the new Defender pisses all over the old Defender if you wish to go lightly off road (check latest review videos) it'll be safe, comfy along with a better transmissions, engines and you could drive the length of the UK and be able to walk after wards.
The folk that buy a late Defender XS (or similar higher trim level) 9 times out of 10 wont be buying it to go off road,a farm hack or as a work truck. It''ll be for urban usage and maybe some towing. So surely you would spend that money, or potentially less and drive away a brand new Defender from the dealership? Thus decreasing the demand for the later classic Defender?