When my former, overbearing and abusive boss was away, her boss would come around and talk to all of us in a similar fashion. He knew she was abusive and overbearing and took the opportunity to gather information (he was a little afraid of her too). The problem was, when she returned, he'd meet with her and confront her with a list of grievances in such a way that she easily figured out where each complaint came from. So my experience tells me he's on a fact-finding mission about your boss. I honestly don't see a boss telling an employee how critical they are to the business and then firing them. Since the meeting is making you anxious, could you talk to him and ask if there's anything you can do to prepare for the meeting, or ask to push it up before the weekend? Nothing wrong with being a little proactive!
Just my two cents...
Nellie