These are the only required routine pilot/cabin communications at my airline:
Prepare for departure - Before takeoff
Passing 10,000 feet in climb - chime
Prepare for landing - Top of descent
Passing 10,000 feet in descent - chime
We have no requirement at all for the cabin crew ever to contact the pilots under normal circumstances.
Some of the old INS navigation systems without a full function FMS would go into holding upon reaching the last loaded waypoint, but newer systems go into heading
AFAIK.
On the A320, the FMS flight plan almost always has a discontinuity at the end of cruise. Arrival procedures usually terminate with a fix or a heading, followed by a discontinuity between enroute navigation and the approach procedure, the idea being that ATC approach control will provide vectors to the final approach course when the aircraft is in normal proximity to do so. This allows ATC to manage the flow of traffic and provide normal spacing for arrivals.
At the discontinuity point, if no further routing has been entered into the FMS, or the mode of navigation has not been changed by the pilot, the aircraft will fly the heading it was on, while reverting to heading mode from NAV mode with a chirp, and continue to fly that heading. This rarely happens. Normally before reaching that point, ATC will have issued a vector or the pilot will querry for one. If the arrival procedure ends with a heading rather than a point , not uncommon, the aircraft will fly the heading and again, the pilots will querry if further instructions are not issued before flying too long on that heading.
Generally the system works very well.