Exactly the same thing happened to me a couple of years ago when I found out eight months or so before the warranty on my first pump ran out that "policy has changed". In my case, I was looking for both a replacement pump at the end of the warranty period AND a decent choice of replacement and although I managed to make progress on the first issue, it took a further 9 months to resolve the second. (I am now a happy bunny!).
After a lot of letter writing and conversations with folk in my NHS trust, I got the impression that the policy change was down to the medical directorate - doctors in the diabetes consultancy hierarchy - rather than what became the CCG, no doubt because of budgetary challenges laid down by the latter.
I would be careful not to get too emotionally charged in any letters and simply present the facts. Specifically, I would avoid phrases like "...it's essentially playing russian roulette with somebody's life" as the comeback is simple: "No it isn't, you are provided with backup supplies of long acting and short acting insulin which can be used during the time it takes to obtain a replacement pump".
If you were told that you would get a replacement after the warranty ran out, say so and make the point that this was one of the reasons you accepted the switch to an insulin pump.
Let me know via a PM if you wish to discuss this with me - always happy to talk on the telephone, when convenient, if it helps.
Alan