I had that problem yesterday, well, kinda. There was an option to exchange vows and kiss, which they did, but the activity wasn't ticked off in the list of wedding activities, and when I checked their status after the wedding, I found out they were still engaged. So I clicked on the arc, saw the option "marry Sim" and clicked it. They did get married then, thanks to that, but by that time, all the guests had already left.
Weddings really are such a hit and miss. The last one I did was SO annoying. Guests showed up late, including the bride's mother who was also supposed to officiate the wedding. We're talking hours here. The bride's mother arrived when the ceremony was all but over, and at least the guests remained mostly seated throughout the ceremony. But it takes them forever to react to prompts or go to where they are supposed to go, e.g. the dance floor, or that champagne bucket. You have to time those activities carefully and give the guests time to react. Otherwise, if you, say, click on "throw rice" once the guests are outside, they might do just that, but not right on the spot. No. Last time, they followed the groom outside and straight into the building where the restrooms are because he needed to use one. They threw that rice while the groom was in the restroom 🙄
And don't get me started on the clothes. Most of the Sims at my last wedding were Sims I created for the various households I play rotationally, and in the past, wearing whatever I had picked for them never was an issue. This time? One of them showed up in a military uniform even though she's a chef, the bride's older brother wore a sweater with a scarf, and one of the bride's friends showed up in a white flowing gown that looked very much like a wedding dress. The bride ended up kicking her out for that.