>why did artist published exactly same manga Because the coloring process for those magazines are done by some low-paid workers and its quality is totally amateur. I guess the artist wanted to prove that their "original" work is not as bad. Sadly those fake full colors appeal to masses (especially phone users).
Depends on whether the artist is interested in continuing the story, whether publisher wants a continuation, and whether or not the author is in trouble for publishing this on his own outside of the magazine where it appeared (I don't know what the terms of their contract is, but usually the publisher holds the rights to the material that they publish).