It's not good. You might be ok if it's in an unstressed area, but it's pretty bad most of the time.
Yes
Are you talking about a crack in the engine block? Sorry, it's not repairable.
yes
It should not
no
If ice forms anywhere in the engine, it can crack the block.
Most definitely.
crack the engine block and oil mixes with water or antifreeze.
Antifreeze helps by not allowing the coolant to freeze and possibly crack the water passages of the block.
Lack of anti-freeze in sub-freezing temperatures. The water in the block freezes and expands.
Yes.If you have no antifreeze in the radiator or engine,sometimes it will freeze.Usually a freeze plug in the engine will pop out before any major damage is done. Sometimes the block will crack,or the radiator will crack or burst if no anti freeze is in the system.
The repair is most likely more money than the car is worth, you need a new engine block.