After LTD payment stops, then what?

As per my benefits agreement my LTD stopped when I turned 65. As a result my CPP-D automatically converted to regular CPP. I do NOT receive any payments from my employer or insurance company at all. Recently I was contacted by employer asking when I will return and if I have updated medical. Can they pressure me for medical or to return?
I am having many symptoms and am not able to return at this time. What rights do I have?
Thanks