Wifi still going dead on upgrade from iOS 6?
No-one here can give you a 100% definitive answer to a question starting with Could... (if you get what I mean).

However, what I can tell you is that in most cases where an iPhone's Wi-Fi has seemingly stopped working after an iOS update/upgrade, they can be readily resolved by the user. In those rare cases where the issue has been hardware related, the iOS update/upgrade has only acted to aggravate a pre-existing problem.

If you have a compelling reason to upgrade your iPhone 4 to iOS 7, then do it. However, as always, be sure you do a full backup first. Also, in case you aren't already aware, the latest version of iOS officially supported on the iPhone 4 is iOS 7.1.2.

Finally, if you do decide to upgrade and find you do have issues with your Wi-Fi, then feel free to post another question here for help.