Caught a swarm on 24 September in Alentejo — can a swarm this late survive winter, and how much do I feed it?

A neighbour rang yesterday about bees in her olive tree. I expected a wasp nest; it was a proper swarm, maybe two kilos of bees, calm and hanging in a tight cluster. Shook them into a five-frame nuc box with two frames of drawn comb and three of foundation, and this morning they're still there, fanning at the entrance. Six years in and I've never had a swarm this late. My guess is it's not a real reproductive swarm but a colony that absconded — the summer was brutal here, the last flow ended in July, and I've seen wasp pressure at my own hives. I haven't found the queen yet. Question for the group: is it worth trying to winter this? Alentejo winters are mild, we rarely go below 5°C, and the rosemary starts in January. If yes, how hard do I feed — 2:1 until they stop taking it? Or is the sensible move to combine them onto one of my weaker colonies?