Rather than resigning, I probably would have battled on regardless (would you?) You never know, the computer might then have made it's own mistake (especially if you believe the conspiracy theory that IBM had a team of real people actually deciding the moves for the computer!)
I expect the resignation may have been influenced by Kasparov being a bit tired of playing by then, & also his annoyance with the whole human V computer set-up.
So ichwar, did you know the answer to the 3rd part of the question?