From a pharmacy viewpoint, insulin lasts quite a bit longer than 90 days from production, if kept reasonably cool. But the clock begins running once it's in use by the consumer, or unrefrigerated. Then it's about a month, IIRC. There are handy evaporative pouches (Frio brand, for one) to keep insulin cool while traveling, away from refrigeration, or in case of power outage. Nonetheless, in the case of a total collapse, lots of diabetics and others dependent on one thing or another would inevitably die, if none of the other potential causes of death in such an event didn't kill them first.

I have to also wonder how all the schizophrenics, severe depressives, others with various medical conditions, and drug addicts, who require medication not to maintain their lives, but to sustain their ability to function effectively, might fare in a total collapse. Darwin can be a harsh master.