You can keep your Gmail account forever and transition to a new email in a slow pace. By auto forwarding your Gmail to your new account, or if your new email can act like POP or IMAP client to access your old Gmail, this process is painless.

I had a Gmail in the month it was launched and I switched to my own domain (ironically, still in GSuite) in a process that took a few years. Whenever I login into a site with my old email, I would update it to the new one. My current email still connect to my old Gmail over POP3, but it’s mostly empty.