two possible outcomes since we still have till ch 204 i guess:
1.)the series ends in a few chapters.
this is shounen jump, so basically tanjiro may have a chance to survive. either:
1.a.)the reason why dad told nezuko to save tanjiro is that he will definitely become a demon. if nezuko will do what tanjiro did from the start of the series then, everything will end in reverse. nezuko will vouch for tanjiro that if she returned to being a human, then tanjiro can do it too and will not harm anyone. if this works out. yushiro can make a drug that can turn tanjiro into a human someday. the series ends in showing the aftermath for each character.
1.b)tanjiro regains his senses and asks everyone to end him. then giyu having the resolve to protect everyone and thank tanjiro, will give the final blow by using "go no kata: kanten no jiu" to painlessly end tanjiro's life.
2.)the series will have a sequel/spinoff
2.a)GOOD ENDING +SEQUEL
(this branches from 1.a. ending)
nezuko will beg that they must not kill tanjiro. sakonji can use suggestion to tell tanjiro that he must protect humans. i think there's reason why wani sensei turned tanjiro into a demon. what if there's another threat greater than muzan who has access to the blue spiderlilly and can create hundreds of muzans? if this is the case, sequel can have demon slayer nezuko, pillar inosuke, pillar zenitsu, pillar kanao, and tanjiro can be the first demon pillar (secret weapon, that will only be deployed when necessary).
2.b) BAD END + SEQUEL
just like in yugioh gx (hao the supreme king), tanjiro will become the demon king. same with 2.a ending, well have demon slayer nezuko, pillar inosuke, pillar zenitsu, pillar kanao etc, in a quest to save tanjiro either by turning him into a human or turning him to dust.
BONUS:
worst case scenario:
almost everyone dies and someone, probably kanao delivers the final blow, defeating tanjiro. at the end of the series, tanjiro will repeat what he said via monologue: "when happiness disappears, theres always a scent of blood"
