My employer did not terminate me after 90 days long term disability. If I try to go back now, can they refuse?

My employers are high profile nationwide worldwide company. I know I am legally still their employee, because sometimes I receive a bonus in my direct deposit bank account, also, I still have the company insurance. I want to go back to work and being for PTSD for 4 years. I fear they will refuse me because right before I left, I complained about a job they took me off of, even though I was doing very good and responsible work, so they told me. My employed took me off a job position because they said they were changing the job classification. I found out, only by accident, the job was given to a new employee, 30 years my junior, in the exact same classification. I questioned this at a meeting and they flipped out. I am afraid they will tell me I'm fired if I try to go back. Any ideas?