Jason Newsted joined as Metallica's bassist after Cliff Burton passed, and stayed with them until 2001. He left on good terms, but both parties had different priorities. Newsted wanted to take a year off and work on a side project, while the rest of the guys wanted to keep going. So, Newsted left. No one seemed to harbor any negative feelings.
Newsted worked in many bands since, and has a new band out called Newsted. Want heavy metal? You'll enjoy Newsted. You can a free download of their new track "Heroic Dose" HERE .