Are there any responsa in the literature that either encourage or require people to maintain health insurance, perhaps as a fulfillment of the obligation to guard one's health, or in line with any other commandments or Torah principles? Of course, this would mainly be relevant in a society in which expensive and effective healthcare is available for purchase (i.e. modern times) and not automatically, universally paid for by the government (e.g. in the United States, and to varying degrees, many other countries).
(Hat tip for the question to William Friedman.)