In current sealed league skirmishes involving ring-bearer should not be possible to cancel (due to a lot of
Incognito/Crouched Down available which weren't meant to do this). A quick fix could be changing format of those games to open (only hurts someone who happened to get multiple Orkish Smiths and wants to play them).
Overall I think ring-bearer skirmish in sealed should be possible to cancel at Fellowship and Towers site path, impossible at Shadows site path, it doesn't matter too much at King site path (though probably should be impossible as well, due to
Slunk Out of Sight).