The $250k is the protection floor, not the ceiling. The FDIC guarantees that $250k, but SVB has assets well beyond $250k per account.

The FDIC is in the business of protecting depositors. So it will pay out the floor immediately as a matter of course, and then will continue to use the tools it has available and the remaining assets of SVB to pay out more — perhaps 100%, perhaps some amount less — to depositors.