A/C blowing hot air. Took to mechanic and...

Yes actually it is the main component of an ac system. Do go to several mechanic to get a diferrent opinion. Compressor do not usually go out, thats why you should get a diffrent opinion. Preferably take it to a mechanic who is ASE certified on Automotive AC system. If the system had not been running for a long time and the hose were disconnected, that is one way a compressor can go out because all the dirt and contaminant can get inside the compressor. Another way a compressor can go out is if someone put too much oil in the system, or the oil has dried up because the system was open, and made to operate without oil.

The compressor isn't necessary at all... you just won't have air conditioning. Half my junk cars have had a dead compressor :)