Is It Ever Okay to Pull the Plug on Life Support?

Questions about pulling the plug on life support, when it’s appropriate for Christians to stay and fight vs. leave, and whether vows of silence, poverty, and celibacy taken by Christian monks are morally praiseworthy.

• Is it ever okay to pull the plug of someone on life support?
• When is it appropriate for Christians to “stay and fight” versus “pack up and leave”? 
• Are vows of silence, poverty, celibacy, etc. taken by Christian monks morally praiseworthy?