I never even tried Inbox because I didn't trust that it wouldn't get killed. Ironically I was just thinking about finally giving it a try since it survived longer than I expected.
Just adopt the new services, and if they disappear, use something else.
What do we exist to persist these days and how long for?
Google have broken that trust on countless occasions, and as a consequence for half a decade they have been deprived of the opportunity to waste any more of my time. You should consider doing the same
If only I could easily use something like notmuch/isync on my phone...