If air compressor for air conditoning goes out can it just be unplugged?

You can unplug it but if the compressor has a mechanical issue, it cold cease up and throw the belt, you lose the belt turn the car off and do not drive it far. A good used compressor is not a bad idea, making sure it is not worn out as well before you put in in. Most the times if they turn freely and don't have obvious mechanical issues, you can save a lot of money and then reload oil and recharge, you'll be happier with ac. If not for ac, your compressor also cycles when you have the defrost on to remove moisture from the compartment