I just made the switch off recently. It actually is a lot more seamless than you'd expect. You can still snooze emails, and then "archive" (mark as done) everything that is taken care of/replied to/no longer needs your attention. Those are probably the two biggest pieces of the Inbox workflow that are pretty much identical in Gmail.

It's not quite as integrated, but all of the pieces are still there. For using reminders, you'll have to use google Keep. And for tasks without reminders, you can use Google Tasks.

On the plus side, it feels like Google stopped maintaining Inbox a while ago and it was getting horribly slow for me. The new gmail is amazingly responsive in comparison. I'm actually glad I made the switch for that reason alone (I had to make the switch before march because the Android Inbox App stopped working - it would crash within second after I opened it every time).