LogFAQs > #976136376

On its own, it wouldn't be hugely detrimental considering there are still three other blacksmiths. You wouldn't be able to get a +15 or divine weapon, but you'd still have access to basically any other kind of endgame weapon. Plus you could always fall back on casting. Pretty sure sorcery catalysts don't even need to be upgraded in DS1.

A no upgrade/repair run could potentially be interesting though. Might get a little tiring taking half an hour to kill every boss (and Four Kings would be a nightmare), but maybe fun if you're really starved for a challenge.