Yes, I was made aware of this via a letter last November:
"We have been informed that for the foreseeable future there will be no further supplies of Insuvet products (Lente, Pzi & Neutral). There is now only one UK authorised veterinary medicinal product containing insulin and this is Caninsulin (Intervet /Schering Plough). Insuvet Lente is a bovine insulin whereas Caninsulin is a porcine insulin, therefore it will not be a simple straightforward swap of the medication,we will need to adjust the amount of insulin given."
As a result, I stocked up (well, I have 2 bottles - incl the one I am using now, and the vet has a spare for emergencies).
I'm very worried about this too, especially as there appears to have been problems with this type in America:
http://animalsheltertips.com/blog/health/diabetic-pet-owners-vetsulin-alert/And, as you say, what happens if an animal doesn't respond to treatment, there are no other options now.
I also have the additional worry of managing the transition myself (obviously with guidance from the vets), as the vet who was looking after Sweep left last year, and I lost some faith with the vet he is now under when she previously advised me to up his dose without testing his blood glucose. I did subsequently query this, but he had a hypo attack the night before I was due to see the old vet for a second opinion. He went into a coma and was in the vets 3 days, and ever since then I have taken it upon myself to monitor his condition with a glucometer at home (only referring to vets when something odd/worrying occurs).
I am dreading the transition.