Terrapinn have put a lot of work into replicating their face to face events online and it mostly works. The plenary events online are, in some ways better than being there live: you can see and hear the speaker better in a video conference than in a large hall. Asking questions is much the same (Terrapinn.com) where already using an online system for curating questions face to face. Round-tables also work well online, where there is a celebrity leading a discussion around a table. I have taken part in these live and they work just as well online.
Terrapinn have also tried to facilitate personal meetings online. Participants put in their details and can use the conference system to contact people attending they know, or would like to know. The parts of a conference which don't work as well online are informal contacts and the exhibition. Part of the joy of a conference is running into people you know and being introduced to their colleagues. I am not sure how to reproduce this online. The other joy is wandering the exhibition talking to vendors and having incidental conversations with people who also stopped at the stands. An example is when I found Martin Dougiamas, founder and CEO of Moodle Pty Ltd, at EduTech Asia 2018 in Singapore.
One problem I have noticed with how Terapin have set up the event is that each presentation is in a separate Zoom conference. Unlike a face to face event, there is not the option to simply stay in the room for what is next. There is the option for each participants to build an individual agenda (I have loaded mine into my electronic diary). However, often at a conference I ask those around me what they are going to next, ignoring everything I have circled on the agenda.