I started my fix gear riding on a geared hub and a BB lockring. Now, in those days, nobody did skip stops. Trashing tubulars gets expensive fast! Never had a issue (except first ride. I forgot, tried to coast and got rocketed into the air by the upcoming pedal. Landed unceremoniously on the road from 20 mph; little speed at impact so no road rash, just bruises and a ripped up internally left leg. That hurt! The lock ring did it's job.

If the lockring did unscrew, it probably wouldn't be a big deal except the rear wheel wouldn't stop you (you are planning a front brake aren't you?) Probably some scratched paint on the chainstay. Maybe some chain damage but probably not. Most likely just a required stop, pull out the wrench, spin the cog back on, remount the wheel, dial in the chain slack and go. When you get home, tighten up the lockring with the spanner. Put getting a real track-hubbed wheel a little higher on the list.

I see the 'never ride a fix gear without a proper track hub" said like the world might end if you don't. Highly unlikely unless you insist on skip-stops. Use decent brakes and the FW hub with a BB lockring should work just fine. I won't ever again but that is because fix gear hubs are now easy to get, I love building wheels, track hub with their wide flange spacing make such good ones and I have had a lifetime's worth of "incidents". But if I were 22 again and wanted to try fix gear and had a FW wheel on hand, I'd do it again in a flash. (That my first ride ended as it did was proof enough that the BB lockring can work rather well!)

Ben