I'm from that generation, all my friends were on MSN. That was the equivalent of Facebook at the time, everyone was there.
It was still not at all what Facebook is. I did school works on MSN but there was no history or always on conversations. We scheduled being on MSN to works on something. MSN was the equivalent of a room.
Facebook is the equivalent of a board, you put it there and you let people read it whenever they want, whenever they can. This is game changer. In University, most of the times, we didn't have to schedule time to works on it at the same time, it was and stayed in the Facebook conversation. It was actually quite rare that we were all on it at the same time.
Same goes for events organization. Never ever would I consider doing that on an IM. The difficulty of an events organization is finding time for all people to come together, you can't do that on an IM. Email could do that sure, but it's a clusterfuck, much more slow paced and people are much more prone to ignore them.
So yeah, IM was part of the solution but their ephemeral natures were a huge issue. Yes there were alternative, but they all came down with pretty issues themselves and one of the biggest, is simply that it wasn't used enough by others. I was barely able to convince people to switch from Facebook to Slack for school projects.