If, by chance, I acquire an item through purchase of prize tokens, and then quit from the Game, will I still keep the item? (ex a Knife of Lost Sky?)
It depends by what you mean "Quit the Game."
If you die or intentionally drop out of the game, yes.
If you simply have no form and just stop playing, no.
That’s interesting - the wiki says you lose your prize tokens and exotica but doesn’t say anything about losing the items you purchase with prize tokens. I have no intention of retiring so am not going to try it myself.
You don’t lose items if you exit the game, although all your tokens are lost.