Of course if it is a autopilot issue we don't yet know exactly what. I'll recount an incident we had on a AS332L some years ago: Approaching a rig the aircraft suddenly started to shake rhythmically. The crew felt there was something dire wrong with the rotor system and warned the pax that a ditching was possible, but in the event they carried on to the helideck. It eventually transpired that a vertical gyro had got a wobble on and this was, through the autopilot, putting in spurious rhythmic control inputs that emulated rotor imbalance.
So faced with a suspected main rotor failure or very serious issue, it is perhaps not too surprising that the crew didn't think of punching out the AP as one would prefer to have as much going for one as possible when dealing with an emergency, as opposed to making life more difficult by killing the AP. In this case it was all over fairly quickly due to their proximity to the rig but had it happened in open ocean, who know what they might have done. It is very easy to pass judgement in hindsight and from the comfort of the armchair, somewhat harder to get it right with a massive flood of adrenalin and near-panic!