Not always, but a broken timing belt can ruin an engine, especially if it is an interference engine. In an interference engine, the pistons and valves share a very tight space at different points in the engine's rotation. When the timing belt breaks, the camshaft stops turning in sync with the crankshaft, and pistons may hit open valves. The result can be bent valves, damaged pistons, broken valve guides, cylinder head damage, or a repair bill high enough to make complete engine replacement more practical. In a non-interference engine, the vehicle usually stalls and will not restart, but the risk of internal damage is lower. Do not keep cranking the engine. Have the vehicle towed and inspected before trying to restart it safely again, to promptly avoid additional damage.