I'm not the only one who has been thinking about what to do about events that have been cancelled due to the new Corona virus. The obvious answer seems to be “conduct them online instead”. However, there's no guarantee that a successful in-person event will be successful online.
Your “online event” is in a completely different competitive space. An offline event competes with other events. Exactly why people go to events is a mystery, and different for every person. Just because they go to an offline event doesn't mean they will be interested in your online version.
If you replace your event with a day of livestreams, videos, chats etc., these things are competing not with other online and offline events, but everything the internet has to offer. Podcasts, blog articles, Slideshare presentations, Udemi courses. If you're assuming people are working from home, then you're competing with Netflix, games consoles, the bath, and the fridge too. You don't have a captive audience, so it's easier for people to drift away and not come back.
I'm quite fatalistic about the prospect of events being replaced by online versions.
I think you need to separate two things when deciding on the future of your offline event: i) are you going to repeat your offline event in the future, once the crisis is over (assuming it ever will be)? In this case, just sit it out and keep things ticking over. ii) What are you going to do in the meantime? The answer to ii) shouldn't be simply “an online event” but something meaningful, or at least an experiment, that offers something people will want (possibly pay for), and will choose to make use of, despite everything else their office, flat, and the internet have to offer.
Fatalism aside, this perspective can open up creative avenues. If you stop thinking about events, you move out of the event-organiser's mindset. Don't ask people “how are you doing events online?” but ask “what formats are there that can leverage my audience, brand, and any other assets I have?” Imagine someone in the setting you want to reach them in. Are they in front of the TV, watching your content on an Amazon TV stick while discussing it in Slack? Are they listening to a podcast you've started? (Which you will have to publish regularly, not just once a year like your event.) Perhaps reading your blog article instead? Are they in a car, taking a walk in the park while keeping a distance of two metres from a colleague they've met for a chat?
There's no guarantee that any of these ideas will work. But there's certainly no guarantee that your “online event” will work either.