Assuming i received my validation stickers, and then proceeded to lose them, what would I do?

go ask the registrar's office for a new one. bring proper ID when doing so

Yep. Its quite easy to get a new sticker by coming to the Registrar's Office. A lot of grad students does this to get double stickers so they can sell one to the undergrad. This is due to the fact that grad sticker are valid year round unlike undergrad sticker.

At what point between opening the letter, and placing the sticker on your card, is it at all possible to lose it? Haha you sir are a beaut!

Just tell them for some reason you received the mail but couldn't find the sticker inside.