It might come back next year but I doubt it will be as prevalent as it used to be. A lot of major influencers like Geoff Keighley were thinking of dropping out before the cancellation news, and we even had Sony drop out completely last year. It seems with the advent of the age of information there is no need for a big event like this since it's much cheaper to broadcast your news on the internet by yourself. Not to mention that big leak that happened last year destroyed the confidence of a lot of industry officials.
A damn shame really because the true magic of E3 happens behind closed doors and not in front of the audience. A lot of companies and major developers met together on this event because it really was the only time in a year where every major gaming company were on the same avenue. A lot of deals and friendships were formed from this event. A recent example of one of these friendships is Microsoft porting their games to the Switch and putting Banjo in Smash.
I never really got the notion that E3 is that easily replaceable by companies having direct-to-consumer announcements whenever they want. Sure, you could theoretically drop a trailer anytime, but would it have the same impact? A lot more people are going to watch a full-on livestream, with many games, than a single trailer, especially if it's a less big game. When you have your trailer in a showcase it kinda elevates it, hell the whole reason we like Directs is because it's tons of news all together, you never know what you're gonna get, and (ideally) there's something for everyone.
Even if companies move to all having their own Direct clones, E3 itself I think makes them all more special. Like, I would normally never watch a Ubisoft Direct because I don't play Tom Clancy games and Just Dance and that's like 80% of their output. But if it's part of E3? Sure, I'll watch it. And I can't be the only one. Compare the 419K views the last State of Play has versus the 2.4M their 2018 E3 did. Even with Nintendo, who has their fans much more pending of their Directs, still has over one million more views between their last E3 and their last (general) Direct.
Could E3 work as just an ESA-coordinated week of digital events, sparing expenses on the stages and such? Sure, for the fans, I'm not going to get into the loss of networking opportunities because others are much better informed than I am. But I don't think E3 will go away because I don't think it's as expendable to publishers as so many are making it out to be.
Also of course Geoff Keighley was ditching E3 dude's trying to create December E3.