Continuity mistake: In the bar scene, Stan has a long stray hair on his left eyebrow. The backdrop is the window and it's easily visible. A few moments later the stray hair is gone.
Continuity mistake: When Alonzo shoots his partner in the vest twice, he injures him on his right side. In the next screen, he is on a stretcher holding his left side.
Answer: They grew sick and tired of Alonzo's arrogance and probably decided he wasn't worth the effort. Alonzo was however killed by the Russian Mafia because Jake was told that Alonzo killed one of their couriers and had to pay them one million dollars by midnight or he would be killed himself.