This is the switch in question. The lower right switch is the one that stopped working. The left (overhead fan) and upper-right (outside porch) switches continued to work.
Inasmuch as the only replacement switches of this type we could find in Fernley were cheap Chinese junk from the local big-box store, Lisa elected to do something more radical and rebuild the entire box so it would accommodate the (not coincidentally, American-made) switches she had in stock.
She located the circuit breaker that includes that switch. Because that turns out to be the circuit that also feeds power to my computers, she ran an extension from an unaffected circuit so I could continue to work at Day Jobbe while she fixed the switch.
Using Wiremold surface-mount conduit and boxes, Lisa rebuilt the first box and put on a second. The original leftmost switch (overhead fan) stays the same. The outlets are not connected to anything at the moment and are there to fill the holes while Lisa decides what to do with that slot. The next switch (left switch on right box) runs the landing light above the front door (the one that failed on the old switch). The rightmost switch runs the porch light.
The face-plates are what she had in stock. She will replace them when we get a chance to buy more parts.
The new arrangement has an additional advantage, in that the switches are now placed relative to each other in the same way someone using them sees the three things they control. Even after several years, I was always getting the the "stacked" switches confused.
Yes, this was more work than just replacing the one switch. But Lisa is much happier with the results.