Story's from MMOS

Why would you want to take a story that you saw in an MMO and put it into your own game? You could of course make a similar story, but taking an exact story would be a copyright violation. If you changed all the details so there were no copyright problems, that would be fine, legally. There aren't that many plot archetypes in existence, and they have all been many times, so it's almost impossible to create a story without it being similar to some other story. But still, most MMO stories aren't very good. The only noticeable virtue they have is already being in a quest format and appropriate for a player roleplaying a warrior character, which most (but not all) game characters are. It could be useful to write out all the dialogue points and quest requirements of one of your favorite quest chains in an MMO, because that would help you see a pattern that works. That would be a similar exercise to outlining a novel to see how a novel plot works; this is an exercise I recommend to anyone who has difficulty writing a good plot. But if you're looking for a source to borrow material from, you might be better off borrowing from an anime, movie, or novel, where the average quality of the material is higher.

I believe/hope the OP is critiquing the bad storylines in many MMOs, e.g. it would never make the cut as a single player game. In many cases I would agree, as most MMOs offer a non-persistent persistent world, e.g. everybody's the hero/nobody's the hero. Normally nothing you can do will truly advance the story, as other people don't want the story advanced for them. One alternative is games where the backstory is provided by the MMO and the story is built purely from user interactions. In either case, unlikely to be considered a worthy story from the MMO. Also MMOs designed to have easily extendable quests tend to err on the side of "errands", e.g. get this and kill this to get paid.

I wouldn't say the storyline in MMOs are bad, in fact some of them have been very good (so yes some of the stories could be converted to work in other games). Their weakness stems from how the stories are told to the player (most often via text) which just doesn't work in a game were you're expected to play for such long periods of time.