Can an employer fire you if you told them you were getting deployed, but they said the reason was for conduct?

The company that you worked for does not have the right to fire you because of your deployment but that does not stop them from firing you for cause and that cause can be just about anything. That company does not have to warn you at all they can fire you at will for any reason except your deployment unless you were under contract with them. In my opinion if you sue them in court you will lose.