I think that this is a question that has a two part answer.
First part: The pure hourly volume will decrease as people go back to work. There simply won't be enough time to put in the same kind of volume for those in this situation. Somebody pointed this out in a previous response in this thread, and this is a good point that should be acknowledged
Second part: The popularity of online poker won't wane, because those who took up online poker who were previously brick & mortar players exclusively won't stop playing online due to the convenience. The one obvious example that comes to mind is Michael Loncar (Twitch Streamer). He was a live player exclusively who made the transition to online poker, though for different reasons (Black Friday in the United States). He acknowledged that he will play live again once it is available (and most importantly safe for him), but he's never going to stop playing online, and has dedicated himself to improving his game.
Now, he's doing this to make a living, but a lot of people who play to supplement their main income will see that playing online is just simply more convenient and the hourly earn is higher (potentially) than live. I don't see people stopping playing online poker once the pandemic is in the rearview mirror, whenever that is.