> Things are going to get missed

Hit the nail on the head here. Things will get missed. The nice thing about Slack is that you can at least catch up with some conversations you missed at the end of day or in your free time. When you miss an IRL meeting, it's much harder to catch up. FOMO will be an even bigger problem when people start setting up meetings, especially ones where you aren't invited to or you can't attend because you're in another meeting.