IF MY EMPLOYER CHANGES INSURERS, CAN I STILL GET HIP REPLACEMENT

I'M GOING THROUGH THE STEPS, TESTS ECT. LEADING TO HIP REPLACEMENT. REPLACEMENT HAS BEEN DIAGNOSED, BUT NOT YET SCEDULED. , BUT MY EMPLOYER IS GOING TO CHANGE INSURERS BEFORE THE SURGERY, WILL I STILL BE ABLE TO GET THE SURGERY OR WILL I BE FOREVER CRIPLED BY MY HIP AND THE SYSTEM. I'M AFRAID THEY WILL CALL IT A PRE EXISTING CONDITION AND THIS IS JUST A WAY FOR THEM TO WEASLE OUT OF PAYING FOR THE SUGERY.
WHAT ARE MY OPTIONS?

HELP!