Like the other guy said, there's no immediate need to delete the account. And someone else wont be able to pick the address up after you, if you do.

I'll probably leave google eventually, as well, but I don't intend to delete my account. The process of using google services less and less has been ongoing for years for me, and I will just use them less and less, until I no longer do at all.

Where email is concerned, I'll just have whatever my new email is pull in my mail from gmail for a while, and as I receive email concerning various accounts to my gmail, that's when I'll go in and change them over to use my new address so the old inbox gets less and less mail.

Then, eventually, when I haven't touched it for years, I might take the final step of actually deleting it. But probably not.