There is NO short answer here. Until terms like faith, repentance, salvation, wayward members, are defined properly, there really isnt any answer available at all, let alone a short one.
Since you WANT a short answer, I will try. Can a true, born from above, Christian go out and live like the devil? The shortest answer possible, is just two letters. The answer is NO. Either they are lying about their Christianity, or they are risking chastening. I have been under chastening at times. I hated it, but it worked on me.
I would say anyone can lose one's salvation by final impenitence.
What does that bait taste like?