Well, with any impact type of damage; the only way to know what is broken is take everything apart and see what is going on. To find leaks in the cooling system; you could put water into it to find the leaks, also put a pressure tester on it and see where everything is leaking under pressure. Fix or replace all the components that are leaking; fill with water to do all the testing, confirm there are no more leaks... then drain the water and add the correct vw coolant and correct amount of water. I would also check and make sure all the fans work and aren't damaged as well; if the fans aren't working well, you would probably end up overheating the engine. You can ruin the engine; if you don't have the cooling system working correctly and fix all the leaks, broken parts.
I've used this pressure tester from harbor freight with good results:
Radiator Pressure Tester Kit
Pittsburgh Automotive - Item#69258
Radiator Pressure Tester Kit
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