Mike & Nicole’s OPP: Bite my Tongue or Tell?

Dear Mike and Nicole,

I went to a holiday party for singles last weekend and was stunned when I saw my co-worker's husband there. He wasn't wearing his wedding ring. The week before, my coworker and her husband were the happiest couple at our office Christmas party. Should I say something to her or not? She is about to get promoted and will become my boss after the first of the year. We aren't really close friends, so I don't know what to do. There are personal and professional ramifications here! Please HELP!