If the insured letter is lost, you will get the amount of money you insured. if you mail something with no price, say, a passport, you'd better send a recorded letter.

如果报价信丢了，你会得到你投保额的赔款。如果你寄无价物品，比如护照，最好寄登记信。

youdao

In the case of insured bonds, where the interest payment is funded by a bond insurer or letter of credit issuer, the default is still the same.

FORBES: Even If A Bond Doesn't Default, You Can Still Lose Your Money