Damn, first an eye, now an arm... I don't think our boy Tanjirou is gonna pull through this alive.
I get the feeling Muzan will be all but dead when all of a sudden Nezuko will appear, and some more drama will ensue. It'll only be in order to save her that the 13th form will finally appear, but with Tanjirou's accumulated damage it will come at a cost. I still can't tell if he survives or not (kind of hope he will) but I know his sword days will probably be behind him -- not that he'd need them.