In the Erickson book "Great Catherine" there is a quote from someone who basically states that the Tsar was removed from the throne like a child being told to go to bed. I found this quite in line w/Peter's character. He never rebelled against Elizabeth. Even though he was heir to the throne of Sweden as well. He seemed to be dominated by strong willed women. Even his mistress. Quite frankly, i think he was scared to death of Catherine because of her intellect. After their marriage he came to her often frantically when he had a problem, knowing she would help him out of it, and then declare it as his own idea.
The book describes him almost as a simpleton as far as politics go. His reliance on Fredrick of Prussia proved to be one of his many undoings in the eyes of the Russian people. So he probably knew from experience, that Catherine far exceeded him as a political strategist. He probably figured by quietly letting the throne pass to her, he would be allowed to leave unimpeded not thinking far enough ahead that in Russian, that simply would never have happened. He seriously misjudged the Absolute rule of the Tsar at that point in time. I feel the throne was in the hands of the guards. Catherine knew this and built up many loyalties, carefully planning for what she one day knew was to come. I think she hoped his death wouldn't be a necessesity, but knew deep down it was going to come down to her or him.
I don't feel he was stupid, just in a situation he never wanted to be in, never had any experience or choice in and in taking it out on Catherine, he did away with would have been his best alliance.