Believe this will come down to state by state but in my state no but after more then 180 consecutive days yes after 365 consecutive days they can terminate your employment. Best to call state unemployment office or seek advice from a lawyer. They can tell you if it's a state or federal issue and easy enough to Google for either. Many people been where you have in your state trust me.
Yes, he could do that.
It depends on the employee, the employer, the industry, and the type of position.
Can the employee perform the duties of the first job? If not the employer has a right to have the job he needs done.
An employee's action during work time are at the discretion of the company
As far as I know, when you are on disability your are to return to your employer with either the same or similar position. They can give away your position, but you are allowed back onto the job with a similar or same position. For example, you stock shelves in a store in Dept A. making $$ an hour. You go on disability and they put another person in your spot. When you return to work after being on disability your employer is obligated to have you stock shelves as before at $$ per hour, but it may be in a Dept B. I hope that makes sense. I would fill out the FMLA form because that protects you.
Yes they can. If it negatively impacts the employee's performance at their Full Time position, they can be disciplined or let go.
An at will position means there is no contract binding the employee or employer to the company. Either party can terminate the working relationship at any time for any reason.
Legally your previous employer cannot give a negative feedback to a potential new employer. All they can do is verify employment, dates of employment, and the position held by the employee.
The only questions that are truly legal are if the employee worked their and what their position was. They can also ask if they are eligible for rehire.
In Canada the Employer can give your position to someone else for the time you are away, but must give you that position back when you return. However, if you are on and off Worker's Compensation then your Employer has a right to give you another position which you can handle with the condition you have. An Employer cannot fire an Employee that is on Workers Compensation.
No, there is no requirement for an employer to 'post' an open position with in management or for workers unless there is a labor contract (unionized work place) in place and the position falls with in that contract
This is for Canada, but I'm pretty sure the same would apply in the US. The short answer is no, because most employers will have an exclusivity clause in your contract that means you cannot work for another employer while you are with them, and you are still under contract while you are on disability. You can probably quit your job while on disability and not be adversely affected, but I would definitely suggest reading your contract before doing this to make sure your employer won't be trying to recoup the disability payments. You might also find that your employer would terminate your disability if you gave notice, although I'm not sure of the legal background to this (employment law is very vague in Canada).