I think there will always be some tiny loyal Unity usergroup that like it because Unity will probably find some obscure niche that every 1/1000th person will appreciate. But for the vast majority its a no brainer which engine to use.
Once everyone who is using Unity finishes their current project I can’t see many going back to it to do the next project.
And the royalties argument for Unity doesn’t make sense at all either, to me at least. No serious game use Unity and they are the ones that might care about the 5% loss of revenue. Casual game developers are happy for any sales at all and the added advantages of UE4 vs a 5% cut in revenue more than balances it out. If some indie makes $1m of a title would they cry about the $50k lost? I’d be surprised if that was the case.