PACE stands for Program of All-Inclusive Care for the Elderly. It’s apparently administered by Medicare? What are the benefits of enrolling in PACE vs. staying on Medicate? If you leave Medicare and go onto PACE, can you go back to Medicare?
From a brief skim of Duckster’s link, it looks like if you join PACE you must give up any other medical plan you have and get ALL your care from whatever PACE sends you.
But to answer one of OP’s questions, it does say you can leave the PACE program at any time. I would suppose that means, if you were on Medicare, you can get back onto Medicare.