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detecting a PD disconnection event

Title: detecting a PD disconnection event

Just to start up another discussion, I wanted to find out how many people would support
the following concept for detecting when a PD receiving power becomes disconnected.

the concept:

1) The PSE is responsible for detecting when a PD receiving DTE power becomes disconnected.
If that event occurs, the PSE must turn off the power within some time frame (100ms to 500ms ballpark?)

2) The PSE may use any of the following methods to detect this PD disconnect event.

        a) the DC load current drop below "X" ma (10ma?)

        b) the ethernet link has dropped out

        c) another proven method (pending discussion and feasibility proof)
                some suggestions:
                1) the AC probing circuit detects when the AC load changes (opens)
                2) the PD modulation heartbeat current ceases
                3) the PD response to a given PSE code is wrong or absent
                4) other ideas


Please voice your opinions on this concept.
The motivation here is to lower the cost of delivering DTE power.

- Rick