You don't remove your gmail account, you remove your Google account. (Yes, I know, they're the same address. But the phone treats them differently.)
And, as hallux said, you don't lose your email even if you delete your gmail account - it's an IMAP account, so the email stays on the server. (Do Google a favor, some day when you have an hour or two to kill - go to
GMail and delete all those 5 year old emails that you'll never look at again. Probably 3/4 of their Gmail storage is full of emails that no one is ever going to look for again.)