I just bought bitcoin from the bitcoin website, and it is taking a lot longer than I expected to process my information and my request and actually send BTC to my wallet. I set the "expire" setting to 1 day when I was requesting in my BTC wallet. What happens if I am paid after the request expires? Is the address no longer used by my wallet? Does the BTC go somewhere else? Or does it go no where at all?
Your wallet will receive the Bitcoin. Your wallet is still watching for transactions to that address and will be able to receive Bitcoin at that address at any point in time.
The expiration is only used as a hint to the sender if you give them the payment request or the Bitcoin URI. It is not part of the blockchain nor part of the address. So if you just gave the address, then the sender wouldn't even know that there is an expiration. The expiration is only used by the client software but is not a hard limit.