From a pure Jewish law perspective insulin isn't really a question. Jewish dietary law prohibits eating pigs, but not other ways of benefitting from pigs^(1,2). This is unlike, say, forbidden mixtures of milk and meat, which are not only forbidden foods but are also forbidden to benefit from. Even if insulin were "eaten", people who need insulin are at serious risk of developing dangerous health conditions if they don't take it, and one is allowed to eat forbidden foods if one will otherwise be in danger^(3). This is without getting into the gelatin debate about whether heavily modified derivatives of non-kosher animals lose their status as being from the original animal--even if it were universally agreed that gelatin and similar animal-derived products are totally not kosher^(4), insulin would be fairly clearly permitted^(5).

As a historical question, though, one could ask whether this raised questions of Jewish law that were posed to Rabbis. The issue here is that unless something is truly earth-shattering, most questions are asked and answered orally. Because there's very little novel in the question of insulin, it's not the sort of question which would necessarily be put into writing. "Can I take this medication without while I will be in serious danger" is an important question, but not one that requires the sort of complex answer that requires being put into writing. There's already discussion in Jewish law from much earlier periods about medicinal forbidden foods, so insulin really breaks no new ground.

I am personally unaware of any written evidence of the question even being asked about insulin, and cannot find any in a cursory search. It probably was asked to Rabbis, but the answers not put in writing. I suspect it would have been asked is that Jews often have an aversion to pork products that goes beyond the technical limits of Jewish law^(6), and presumably the Rabbi would've answered without asking a question of a Rabbi of greater authority (which is what tends to generate documentation of halakhic questions).

So really insulin is not subject to being kosher or not. Presumably Jews asked questions of their Rabbis if they were aware of the origin of the insulin, but it did not generate significant written discussion in Jewish law, probably because it's a fairly open and shut case.

1. There are Rabbinic restrictions on pigs in other ways--there's a general prohibition on making a living by selling forbidden foods, but for pigs there isn't a prohibition on non-eating benefit, which is not really a relevant concern here.

• See, for example, Teshuvot Achiezer 3:61 by R Chaim Ozer Grodzinski, which permits ingesting forbidden foods via a feeding tube because that isn't really "eating". The person who asked the question thought it ought to be forbidden, but R Chaim Ozer disagreed, and I believe R Chaim Ozer's position is the consensus here. Certainly an injection is far less eating-like than a feeding tube, and a fortiori should be permitted.
• For diabetes in Jewish law as a dangerous medical condition, see, Peninei Halakha, Zemanim 7:5, which rules that diabetics can eat on Yom Kippur to manage their insulin levels--eating on Yom Kippur is a much more serious issue than eating non-kosher food, generally speaking. Or R J David Bleich's Survey of Recent Halakhic Periodical Literature in Tradition, vol 41, No 4, discussing a diabetic person testing their glucose levels on Shabbat, which is also (potentially) a more serious issue than eating pork. While it discusses ways to minimize the prohibition and some academic questions, the fact that diabetes is a dangerous health condition if left untreated is simply stated as a given.
• Which is the consensus position in the US nowadays
• See, for example, this discussion of medicine and kashrut from the Chicago Rabbinical Council, which rules that gelatin capsules may not be taken to relieve discomfort, but may be consumed to alleviate a serious medical condition, and that non-gelcap pills may be taken in any event. This is even within a frame of reference that gelatin is completely forbidden, and that gel caps are considered "unusual eating" (as opposed to not being eating at all, as is the case according to the cRc for other types of pills)
• See here, for example