Let me see if I have this right. You are pretty clear that everything was good when you went to bed. Next morning, you get up. You check on the smoker. The smoker has gone out - it is not providing heat. You check the meat with a probe and the meat temp is still 168, right?
Now, all I've done is repeat back to you what I understand you said. If that is how everything happened, then yes, your meat is just fine. If your meat had been 30 degrees cooler, there might have been some reason to doubt, but 168 F is fine.
Also, I am assuming you didn't leave it out cooling (for more than an hour or so) after cooking. The rule-of-thumb for the danger zone is 40F - 140F. There is a very similar question, with an answer, in this question.