Hops can propagate from live (not 100% dead) foliage.
However, I have found in practice, that the stray bines are more often attached to long, horizontal roots.
Each spring, I dig a few feet away from the rhizomes in my garden to cut out these roots and keep everything contained. The length of the horizontal roots seems to be variety dependant. My chinook doesn't seem to send out any. Nugget and cascade, on the other hand, will send out "runners" 10-15' long.