Always put yourself in someone else's position to know the answer. If you were the wife, would you want someone to tell you? If so, then there's your answer.

There used to be this show called "What would you do?" with all sorts of scenarios, some extremely dangerous like a guy noticeably putting something in his date's drink and her starting to slur her words and trip over herself saying loudly how sick and tired she suddenly felt, and him saying loudly how it was time to take her home (both were actors). No one said anything- even the bartender. The man got up to go to the bathroom leaving the girl alone with all the witnesses, and the closest thing someone did to alerting her is a woman said, "that guy's no good for you."

When asked, they all said they were minding their own business, or some shit like they didn't know the entire story (even though they all admitted they watched him put something in several of her drinks- what other story do they need?).

People almost always intervened in scenarios were someone was being treated unfairly due to their mental status (a person with Downs), a mixed race and a gay couple at a restaurant, an old woman not moving fast enough, etc. But not in any of the scenarios that actually had serious consequences, in some cases putting other people's lives at risk (like pilots getting drunk at a bar and saying they are off to fly- again, actors, but no one stopped them or called to alert the FAA). I see your story as being part of the more serious scenario when people some how think they should mind their business when in reality, so much is at stake by not saying anything.

I live by the golden rule, and minding your own business whenever there is obviously something going on that's unsettling or clearly not right is really just choosing to be selfish and ignoring someone else's obvious need for your intervention or help.