Nintendo has already said they plan on releasing first-party stuff on 3DS beyond 2019. They have at least one announced title for 2019 (the Mario & Luigi 2 remake), and they still have to bring over Yo-kai Watch 3 and Yo-kai Watch Busters 2. The 3DS isn't dead, and it most certainly isn't dead and buried.
Atlus is definitely bringing this one over (unlike EOX).
Software and hardware sales are showing that is dying faster than Nintendo thought. In 2019 will be buried.
Nintendo 3DS
Q1FY2018 (Apr - Jun 2018):
Hardware: 0,36M (Goal: 4M)
Software: 2,95M (Goal: 16M)
Hardware per regions:
Japan: 60k / 24,76M
Americas: 200k / 25,37M
Europe and others: 100k / 22,76M