Actually looking at this, it'll probably end with Muzan dying but as a form of last second revenge, he'll manage to fully turn Tanjiro and since all the demons die when Muzan dies, Tanjiro will start to die. However Nezuko comes in and saves him and also saves the rest of the infected and everyone returns to being human, except Muzan and Yushirou. Yushirou will probably choose to live just long enough to make sure there are no more side effects or demons and then attempt to commit suicide to be with Tamayo. However all of the friends he made in the Demon Corps will beg him to not give up the possibility of living a new life as a human and he'll relent and turn back into a human and live the rest of his natural life as one, perhaps after remembering something said by Tamayo.
