How long can a swarm survive?

[The Bix]

If they don't find a new home, how long can they last?  The reason I ask is that I caught another swarm on Saturday night, when I asked the homeowner how long they'd been there, she said "a week".  I was amazed by the length of time, but even more so when one considers the weather we've had.  Until Friday morning last week, we had lows in the low thirties and Wednesday we had snow.   There were a lot of dead bees underneath this swarm, but mostly they were still intact.  Here's a picture I took from the morning after the snowfall last Wednesday, the snowstorm that the bees lived through hanging from a low tree branch.

[Finski]

.
The swarm has 3 days food with them.