No, the wifi commands should still work, that is compiled in when you use the Arduino IDE. All that has really changed is that instead of loading it over the air via particle, the code has been loaded directly onto the oak via serial. As long as the Oak was configured to be able to access your wifi network (i.e. you gave it the SSID and password in config mode), then that could should be connecting to particle, publishing one message in the setup loop, and sending another every 10 seconds after the led blinks.
I can't remember if confg mode (P1 to GND for 2-3 seconds when powering up the Oak, and then removing the jumper) still works after a serial upload, but it might be worth running through config mode again and seeing if SoftAP can configure your wireless (and apply the settings again). If not, then yes, try doing an manual (serial)l firmware update again to put it back to normal.
However, since it is the 1 out of 5 that is misbehaving, it unfortunately is sounding like a faulty one. Some test code that makes it scan your wifi environment and/or attempts to connect to your router with hard-coded credentials would put that theory to rest, but I don't have anything that is Oak-compatible handy.
