If you wish to continue using your web hosting service then it is best to renew before the due renewal date. The web hosting service will continue to run from the original expiry date not the date that you renew, so you will not lose any web hosting days by renewing early.
If the web hosting service is left to expire and the actual domain name is still active with us then the account will be automatically downgraded to a forwarding account and any web hosting features that you had set up will cease to function i.e. any POP3 mailboxes, MySQL databases etc...
If the web hosting service is left to expire and the actual domain name is not with us then the account will be automatically deleted and any web hosting features that you had set up will cease to function i.e. any POP3 mailboxes, MySQL databases etc...