It's easy when a satisfying manga ends: I archive it and keep a copy to reread from time to time. And if it's such an awesome manga, and art is good, I buy the volumes.
Question is, what if a manga ends, and you were quite invested in it, but it went awry, or the end was not what you liked it to be, or... you just can't reconcile with the last chapter. Do you delete the manga from your archives? Do you forget the story? Or do you keep it (in your harddrive or good memory) as it has kept you entertained anyway except for that ending?
i imagine a better ending in my head .i fantasize
Still keep it. Could reread favorite scenes and arcs as well.
I don't think the ending of a manga delegitimizes all the chapters before the ending.
It's like if the whole manga was great, but some chapter in the middle sucked, does that ruin it? No? Then why does it matter if the bad chapter just happens to be the last one?
I only keep mangas I like very much, when I don't buy them. The rest, even when the end is good, I delete to release space in my HD. From time to time, I upload them in the cloud to release space as well.
I usually weep bitterly once it ends and then think hard about it and crey somemore (if its good).
Unless it is utterly unbearable, I'd just move along with my life and pick another manga to soothe my anger/sadness. Thankfully I haven't found one so all is well for me. I rarely save any Manga in my HDD, but I collect many physical copies. It seems like I am wasting a lot of money if I throw them away simply just because I don't like how the story progresses. Bad memories are still memories so there's still emotional attachment and nostalgic value for bad manga, I suppose. Better to remember the name of the authors who created those bad mangas to prevent reading anything made by them again.
I feel like its a rarity for a manga series to finish while I'm still invested in it. Either I eventually lose interest in manga that are still ongoing, or I read manga that's already completed.
I think I agree with DoctorApollo the most -- a bad ending shouldn't take away from the enjoyment you had from a series otherwise. I do think there can be stages of denial though. Like initially you might feel a sense of "betrayal" from an author for pulling such an awful ending on you. And you may be tempted to just forget that series all together.
But...I always question people that do that. Because authors are just like everyone else, they make mistakes, and at the end of the day, they can only write one ending out of a 100 different endings. The official ending is a suggestion, I think, not a rule. Or at least, this is why I have a habit of not reading the last chapter of a lot of series I finish. >_>