No, insuring against an inevitability isn't silly because there are other factors to consider. Like when the inevitable occurs. Insurers are taking a risk that you put more in before that happens.
Lots of times insurance companies only end up making a profit from investing (that is, they pay out more in claims than they take in premiums but make up the difference by investing wisely).
A friend of mine uses the analogy of "food insurance" to describe the dysfunctional nature of attempts to insure against the inevitable.