Currently Being ModeratedJan 4, 2013 10:13 AM (in response to BethPNW)
I think it would delete the messages.
What I would try is to "deactivate" the account via the checkbox at the top of the Accounts window, Accounts Information, of Mail Preferences. Then I would create a new mail account to see if that works. Deactivating an account should not result in anything being deleted. You can reactivate it with the checkbox and everything should be as before.
You could also copy everything to a mailbox "On My Mac", too. Those messages would then be stored on your mac and not be deleted when you mess with the account.
Currently Being ModeratedJan 4, 2013 10:12 AM (in response to BethPNW)
Comcast is a POP account so the mails are already 'On Your Mac' and will be deleted if you delete the account.
Export your account to the desktop first or you will have no mail after you delete the account.