Are you sure it lost its polyps? Maybe they're just retracted.
Leathers like stable tank conditions as well as good water chemistry. Doesn't have to be super clean, just stable. If your leather is irritated it might not put out polyps for a couple weeks, this won't kill it though.
But if you put it in a spot that has good flow and its not being stung by anyone else it should open its polyps within a week or so.
I've never seen a leather actually "lose" its polyps, so I wouldn't worry too much.
When I first started, I had a sarcophyton in my old 58 gallon with so/so flow, mine would shed about once a week. But if you keep it in med/hi indirect flow they usually get rid of their mucus membrane constantly and won't need to close up and shed. Most leathers like med/hi light as well.