1) Nintendo NEVER left E3. They still have the biggest booth at the convention. The only thing that changed is the format of their presentation (from live conference to video presentation). And it's still called the "E3 Direct". That's it.
2) I disagree. The week of E3 is by far the week of the year with the most gaming related announcements, by a WIDE margin. Attendance for E3 2018 was the highest since 2005 as well.
What more than likely is the case, is that Sony doesnt have enough to show to justify a conference. Rather than put out another lackluster show like last year's, they decide to pull out for now, and come back E3 2020 with a bang, with two years worth of announcements.
Either that, or they are saving for PSX 2019, which this falls within the week of Playstation's 25th anniversary. They will be back at E3 for sure next year.
Bet with Intrinsic:
The Switch will outsell 3DS (based on VGchartz numbers), according to me, while Intrinsic thinks the opposite will hold true. One month avatar control for the loser's avatar.