Sure. 'Dragon Ball Z Abridged' is quite well-known. It condenses the story and adds comedic elements to make it more entertaining. There are also others like 'Naruto Abridged' that have their own fan bases.
For the most part, no. Manga creators usually want to deliver a coherent and focused story without the distraction of filler episodes. This helps maintain the integrity and appeal of the series.
The ending of a manga can be anything. It could be a resolution of all conflicts, a new beginning for the characters, or a surprise twist that leaves you thinking. Different mangas have very diverse endings.