For some reason, my Pleasantview just disappeared out of existence, and does anyone have a backup default copy?

As far as I know, there is a default template in your Program files...but everyone would just advise you to go for clean templates in any cases.

If your hood disappeared it was probably highly corrupted. Do you have the essential mods? Do you know all the major ways that you can corrupt your hood so you can avoid doing them? Unfortunately all pre made maxis hoods ship already corrupted. As Rosebine suggested you would be better using a cleaned up version. if you don't want to do that and simply use the game one you don't need anyones backup copy, you already have it, right there in your installation files. http://simswiki.info/wiki.php?title...t_Neighborhoods

Yes I agree with joandsarah77 get the important mods to help protect your game and read what can cause corruption in your game. ( I know you hate to start that neighborhood over, but sometime it's a must ) also you can get Pleasantview neighborhood here.
But please READ EVERYTHING THERE, you can get an empty template ( That would mean No Sims ) or get the Template with all Sims Character there in Pleasantview. I personally prefer that one and I do have that in my game.
As well as the University I wanted with characters and a Downtown again before you decide read everything there it's very important. Here the link https://meetme2theriver.livejournal...?thread=1995574