How long must I hold an employee’s job for them if they are out on disability?

It really depends on the underlying basis the employee is out on disability. With 20 employees you are not subject to FMLA. You may be required under the ADA to provide reasonable accommodations to the employee. If your employees are unionized, then you should first look to the collective bargaining agreement. Another consideration is what, if anything, have you done in the past with similar situations.

I don't believe the FMLA applies to you since you do not have 50 employees. But is the disability a result of a workplace injury? Then you may have a worker's compensation and retaliation issue. If it is unrelated to the job, then I think you can terminate them for being unable to perform the duties required. I would not fight the unemployment claim however.

I do not know the answer to this question. If they are on disability due to workers comp, you do not have to hold the job open, but there are consequences. Consult with a W.comp attorney or your W.comp insurance carrier. If they are on disability, as determined by your health insurance, I do not believe there is any legal requirement that you keep their job open at all, but I am not sure. If they are on FMLA, the answer would be different.