It turned out my library (Toronto) did indeed expire my card. I shlepped into the main Reference library this afternoon with my card and a copy of a recent Hydro bill (to prove residency in the city) and click, clack my card was restored. The library is only open 3.5 hrs on Sundays but it was pretty busy at 2 pm.
Anyway, mystery solved. And I, too, did not receive an e-mail warning me.