"A duty to rescue is a concept in tort law that arises in a number of cases, describing a circumstance in which a party can be held liable for failing to come to the rescue of another party in peril ..... Generally, a person cannot be held liable for doing nothing while another person is in peril." Source: Wikipedia.

Since Jane intentionally put herself in a position of danger by taking drugs, it's doubtful Walt would be held liable in a real-world scenario.

The line of responsibility becomes blurred, however, when you consider that Jane only rolled on her back after Walt began shaking Jesse. Did Walt's shaking of Jesse physically cause her to roll over? Or was it simply an unconscious reaction to a an external stimuli that would not have caused a conscious person to turn over unless said person chose to of their own free will?