Depends on the nature of the light. If it was a remodel can you can remove the trim, remove the fixture, unhook the wires (better make sure the power is off) and install a box for the pendant (probably will need to do some finish patching).

If it was a new construction fixture (and you can't get into the space above, like through the attic) then it's going to be harder to do.

Why in the world would lights be installed in such a fashion that you couldn't replace it? What if one of these can lights goes bad? What is different about these lights as opposed to some of my other fixtures which my DH has already replaced?

Eh? I've never had a recessed fixture "go bad".

I don't know what your husband has been doing in other cases, but a remodel can actually installs through the hole in the ceiling so it can come out that way.

A new construction can is attached to the framing (typically) and the hole is purely to let the light into the space below.