I don't think I'm wrong in saying that as it simply cuts straight out it is an electrical fault. Others may have alternate possibilities?
There's no spark plugs or anything on the diesel engine - if the engine's turning and diesel is flowing then the engine will continue to run - therefore for it to stop diesel is not getting into the engine. On my L Series, for diesel to be flowing all that is needed is for the pump be pumping. On your TD4 it needs the pump to be pumping and the injectors must be told to open at the right time. The pump (I would presume) is purely mechanical - if the engine's turning, the pump is pumping - there wouldn't be anything electrical to stop that (even if I'm wrong and the ECU can alter the amount its pumping, I would have thought it would pump 'some' fuel). So the injectors are not being told to open - they are not letting fuel into the engine.
Especially as you have a manual (which will keep the engine turning if it turns off until the car comes to a halt), this isn't a tiny 'little blip' of a fault - ie its not just turning the injectors off for 1 turn of the engine. If that were the case, you would have a very lumpy engine (a misfire) that would ultimately continue to drive the car. So for this reason, and the fact that it starts straight back up 100% of the time, I don't think its a fault in the wiring (harness) to the injectors - which is a common problem with TD4 engines I believe. The fault is further 'back'.
Coming back from there then - you get to the engine's ECU. This does have the capability to simply turn the engine off - ie not tell the injectors to let any fuel into the engine. The questions therefore is why could the ECU be doing this? Usually the only reason of course is that it has detected that you've turned the key to the 'Off' position! You're not doing that. There are a myriad of sensors on the TD4's engine the ECU uses to control when and how much fuel the injectors allow into the engine. Most of these would NOT result in the ECU simply turning off the engine - if things got bad enough, the MIL (engine) light would be lit on the dashboard - but the engine would run to some level of performance. For that reason, I can't see how changing the MAF sensor is going to change things (I had a Disco with a faulty MAF and it did stall the engine at times - but most of the time the engine just didn't perform very well!).
One sensor that might have the capability for telling the ECU to not deliver any fuel I suppose is the Crank/Cam position sensor. If this simply turned off (ie intermittent fault) the ECU wouldn't know where the pistons were so wouldn't know they needed fuel. I would have thought though that the ECU would be 'clever' enough to 'try' to keep the engine running and would have thrown the MIL light and a code would have been read by the diagnostics machine.
So we can rule out sensors feeding the ECU with misinformation. What we can't rule out though is a fault with the ECU. They are computers and we all know that they can simply 'hang'! With ECUs though they don't usually hang like a PC does - but they can develop physical faults that triggers a 'hang'. This is a possibility for your problem - but I think unlikely - and the cost of replacing it (together with the security CCU, keys etc) means I think other possibilities should be looked into first.
So why else would the ECU stop the engine? If it lost power it obviously couldn't keep the engine running. Its worth checking the battery connections - but if they were lose, you would have troubles starting the car. The alternator or the battery may be doing funny things with the supply, but no other signs of this. So probably not them. It could be an intermittent fault in one of the wiring looms that the ECU is on. The P1602 code you got might indicate that this is a definite possibility. However if this is the problem, its a needle in a haystack and would probably need quite a bit of an auto sparky's time to identify the fault, if indeed there is 1 - as it starts fine 100% when restarted, I'm thinking not.
So we come back to you turning the key off!
You're not doing that - but if the switch was faulty and ECU detected that the connection to the 'Run' position dropped, it would turn the engine off. Resetting the switch by turning it to the Off, Start then Run positions again probably gets the engine running till the switch drops the Run connection again.
So, if you've read through all this drivel - I wouldn't worry about your MAF sensor (unless there are other issues) and I'd get a replacement switch for an auto sparky to fit - or have a go yourself. I'd be amazed if the switch was a part of the barrel - hopefully its a plastic block that clips on the end of the barrel.
