Well, we can make Numidians even with guilds if we have no iron connected ( and if we have HBR , OFC )
Well, about knights getting obsolete ... the online resources here in CFC say that Knights upgrade to cavs, so, if that is true, we can build knights until we can get cavs. I'm not so sure on this, so I'll check it when in a civ-able comp.
EDIT: the CFC source, as usual, is wrong : knights upgrade to cuirs. So yes, nocho, we will be unable to make knights ( and numidians ) as soon as we get MT + gunpowder.