Does it starts reusing them from the beginning again? Or does it keeps generating addresses 1000, 1001, 1002, etc?
If the latter, what are the implications for when you restore from your hdseed? Do you need to take extra steps to make your wallet aware of beyond 999 addresses?
What's the Electrum behavior for this? How many addresses it generates by default?
What’s Bitcoin Core behavior after running out of the 999 receiving and change addresses it generates when creating a wallet?
from Bitcoin – The Currency of the Internet