Is it legal to be fired after 10 years due to their so called reduced revenues without notice, no cause, and no severance?

Yes, completely legal in GA. There are some federal rules on large layoffs, but not when impacts only a few employees.

Yes, an employer may terminate any employee for no reason at any time whether they have been there 10 days or 10 years. Sometimes, one can assert there was an Employment Contract if there are memos and writings indicating a promise of employment in exchange for something you waived or surrendered (such as a clear writing that you are not accept an offer of employment elsewhere because the current employer is promising employment for 5 years with a 5% raise each year). If you were terminated because of your national origin, your gender, your race, your religion, your sexual orientation and possibly age, you may have a wrongful termination action. Because you were terminated for financial reasons only (1) Thank Obama for this economy then (2) apply for unemployment.

Yes. They can't afford to pay you any more so you are fired. They could also fire you because they don't like you, you came in late on Tuesday or you wore a purple shirt one day. Other than a couple of states that I am aware of, most states are at-will employment states, meaning that the employee can leave whenever he or she wants and the employer can terminate the employee for any or no reason (unless the termination is because the employee is a member of a protected class, which does not appear to be the case here.)

Yes, the reality is if you can quit your employer you employer can quit you.

Absent any provisions saying the opposite, or a formal contract, including a collective bargaining agreement covering your situation, Wisconsin is an "employment at will" state and an employee can be fired or quit for any reason if it is not employment discrimination. If you need more information there are places you can contact in larger Wisconsin communities to get more information.

Probably but contact an attorney to review your overall situation.

That's certainly the law in most states, Texas included. That's not the law in most countries, but it is here. On the other hand, if you believe the motivating factor to fire you was your age, race, sex, national origin, religion or medical condition, you might have the basis for a legal claim.