I don't know how I would feel to find that I am alone, but I think that when left alone with one's self as we are now, we'd go insane.
Our selves are a derivative of what interactions have taken place between ourselves and others. The "Other" is a philosophical concept formed by Hegel. "Othering" is a term that he and psychologists that followed him used to describe what we do to other human beings. "Othering" is how we establish boundaries and keep others "over there" and justify keeping our distance, or maintaining ourselves as just when "they" are unjust, immoral etc.
All alone, what is to be Othered, other than myself? The proverbial "self" is not the body, but the mind formed through relationships. If there are not remaining relationships established through community, I believe that we'd all commit a justified suicide. I say that as we are social creatures, and we'd feel so lonely, that we'd realize how we'd taken one another for granted to the extent that we'd suffer from a sense of guilt that said something along the lines that "I must have been the CAUSE of this singular state."
Consider this: wouldn't we wonder if it was a blessing or a curse? A: Am I the last one living because of how good I was, or B: am I the last one living because I shut humans out so often that I was forced to live alone to see the greatness of human life as a community?
I think, knowing myself, that B would be my take on the matter. We're just not fit for total solitude. I've even wondered if God (conceptually) created life apart from His own due to His own desire for companionship... something that could admire Him, wonder about Him and discover Him through "The Many". Incidentally, Christ seems to have known in advance that His creation was a suicide mission. As though it was established long in advance that He, too, must die. He'd already suffered loneliness - and it's no real stretch to say that we are only "IN the mind of God," since He is all encompassing... in that light, we may just be the product of an infinite imagination which can experience its SELF, only through manifesting ITS SELF through multitudes of individualities.
With that in mind, if we were all alone, we would be GOD. This is all merely a deduction, so we would be faced with a decision. DO I LIVE, OR DO I DIE. It was asked this way once before: To be or not to be? God is only known by creating something to experience Him. SO, He "is," because we ARE.
alone? VERY LONELY!