Whether it is now or in 10 years, it will happen some time.
10 years is a very narrow time-frame for a collision to happen, even 1000 years isn't even enough for an "
accidental" collision.
The only chance for it to happen in a short period is to
find vulnerabilities in both the hashing algorithm used by generating addresses and secp256k1 (
get the prv key from the pub key);
ex. a sudden "
quantum supremacy".
What would happen then if a payment is made to that address? Will it be sent to the wallet owner who connects to the internet first? Or to the wallet owner who had this BTC address first?
FYI, Bitcoins aren't stored in wallets/clients, it's in the blockchain (
nodes), and to spend it, you need the address' private key.
So, the answer to this "
what if" question is: The first one to make a (
higher fee -> confirmed) transaction can spend the bitcoin.