Here’s a compilation of the “countdown” from Monday’s How I Met Your Mother, where (probably with the help of digital retouching) numbers appeared in decreasing order in the background throughout the episode, starting with the number 50.
People looking closely would realize that the episode was counting down to something, so it was an interesting and effective use of the “easter egg.” It led sharp-eyed viewers to expect that these numbers were building up to something, but those viewers would be if anything more surprised by the ending than the rest of the audience, since it seems like the countdown to a joke or maybe just a private in-joke.
As for the actual ending, I was fine with it. I wouldn’t want to see it end this way every week; that way lies Facts of Life territory. But once in a while a sitcom like this needs to deliver an actual emotional punch and a story idea that really matters to the characters. And since having “heart” or learning a lesson has been devalued by the fact that almost every show is doing it, it seems appropriate that HIMYM (in a season that has been a big improvement over the last one) would try to create a moment that feels more significant than just learning another lesson about relationships.