Well, Since it's apparently possible to send coins to an address that doesnt exsist, What if it gets created later down the road? Would it "pickup" the funds since the blockchain says "100btc to XYZ was sent 5years ago, OH LOOK! Theres XYZ!, Here you go XYZ!"
Above is correct. To elaborate, "sending" bitcoins is a bit of a misnomer. I've even read introductory tutorials that indicate that the recipient must "claim" the receipt. This is inaccurate and misleading. Here's a more accurate portrayal of a transaction: First, presume that you're Bitcoin client has the private key for an address, which has some bitcoin value assigned to it (from some other address, via the very process about to be described). Your client uses that private key to digitally sign a
transaction message, assigning some (or all) of that value to another
valid address. This transaction message (tx) gets broadcast to the Bitcoin network at large, where it is eventually accepted into a block on the blockchain, effectively setting it in stone for all time. Notice that your client did not require any knowledge of the recipient beyond a
valid address, and there is no
action taken by the recipient. The transaction is an irrevocable record that the recipient address (and corresponding private key) now "owns" (has control of, or "is able to transfer") the specified bitcoin value. The only way to re-assign that value to yet another address is by following this same procedure, which requires the private key of the "ownership" address.
Under the original post's scenario, that private key may be unknown to anyone. If anyone ever does generate that key pair (against astronomically incomprehensible odds), they mathematically and cryptographically "own" (because this is how the Bitcoin system is defined) any associated bitcoin value assigned to them by a transaction in the blockchain!
That was a bit long-winded, but my goal was to provide a more narrative description of the process. There are many more details about how transactions can be signed over, but I hope this helps explain the fundamental behavior of the network.