What happens when an engine lacks antifreeze?
If ice forms anywhere in the engine, it can crack the block.
If you start and warm up your engine: 1) The oil gets very foamy and mucky, and does not circulate through the engine properly. 2) The water in the antifreeze can heat up until it turns to steam, which expands with great force, and breaks some part of the engine. It's best to have the oil changed. That will empty the engine of the oil and antifreeze mix.
If you have water instead of antifreeze in your cooling system, it will freeze! You won't be able to start the car, because the engine is connected to the water pump (which won't be able to move). If you have nothing in your cooling system (no water, no antifreeze, nothing else), then you need your head checked. Your car won't start either.