The web tier status will definitely say 'reinstall required' but it may still work partially, or fully. What might occur is the pages and options may not render correctly since the versions of weblogic will be different, as well as other items and the AM server and web tier may not agree on 'what to do'. Expect web tier to be 'offline'. Do not expect it to fully work, but I've tested them once in a while on mismatched versions, and it did still allow login and some functionality, but don't rely on it or leave it like that, as end users could be affected negatively...
What you can do is wait until the last patch is installed on the primary AM server, and then uninstall/reinstall web tier once, using the last highest version of web tier patch (web tier patches are full installers) saving some overhead.
