Upon her death (assuming no co-owner like FIL), the bonds will be rated at their current market value for any heirs. They can sell an appreciated asset without paying a capital gains tax. Unfortunately, any loss disappears.
If your MIL has any capital gains, selling the Lehman bonds would generate an offsetting capital loss.
The object of life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane -- Marcus Aurelius