The key concern when a truck comes to rest on its roof is:

When a truck comes to rest on its roof, instability becomes a paramount concern due to the altered center of gravity and potential for the vehicle to shift or slide. This instability can pose significant risks not only to the victims inside but also to rescue personnel attempting to assist. As rescuers approach the scene, they must assess the vehicle's condition and ensure it is secured to prevent any further movement that could endanger lives.

While transport of the patient, access to victims, and disentanglement are important considerations in the overall rescue operation, the immediate threat posed by the vehicle's instability necessitates that it be addressed first. Ensuring the safety of the rescuers and victims alike is critical, and stabilizing the vehicle is a necessary precursor to making any further moves to access or disentangle victims. Therefore, the concern of instability takes precedence in this scenario.