a) They didn't open part two with Jonathan Frakes doing the 'Where No One...' speech. Ok, Picard was going to be back next week, but you don't need to tell us that!
That would imply Picard was replaceable... and Patrick Stewart was and is the biggest asset of TNG -- it would have undermined him on a story and marketing level.
But with this episode, let's not forget the dramatic end music! Which was used in a Family Guy cliffhanger to great effect too.
Yes, but wasn't Patrick Stewart considering leaving at the point in time? I remember reading that some where. Perhaps an interview with Michael Piller, about how he hadn't even writen Part 2 yet by the time Part 1 had aired. That was one of the reasons Picard was kidnapped in the first place, so if he didn't come back then he would be a casualty to the Borg and Riker would have become captain. Now that would have been strange. I wonder in TNG would have been as successful as it is.