Hello and welcome, Mary.
A huge congratulations on winning your battle with cancer. My father is currently going through extended treatments, and it is emotionally and physically challenging to say the least.
To answer your question: Pursuant to state and federal law, employers must normally provide up to 12 weeks of unpaid leave to employees who have a serious medical condition. You exceeded that period of time, so the job protecting aspects of the FMLA and state counterpart would have lapsed unfortunately.
After the 12 weeks and you were no longer able to work, the ADA could require the employer to extend your leave as a reasonable accommodation unless it was an undue hardship for them, and providing that you requested the accommodation.
If it was an undue hardship for the employer not to replace you for the 7 months, then they would typically be relieved of their obligation to return you to work following leave.
Here is a link that discusses what is an undue hardship under the ADA:
The employer is not required by law to provide severance to employees, except according to an employment contract or a written policy communicated to the employees. So if there is a policy of paying a certain number of weeks severance for each year of service, the employer should pay that to you if you do not return.
I hope you found my answer helpful, even if the law is not in your favor. I would be happy to clarify my answer if anything is not clear or you are looking for additional information. All the best to you!