Auxiliary circuit to reduce power losses in idle stage of this oscillator (wireless power application)
I think the first step to a circuit like this would be to measure the current through the Lp coil. A current measurement typically consists of a low value resistor and a current amp. The current would change if a receiving coil were placed near the transmitting coil. A threshold could be set on the current measurement (with a comparator)to allow the circuit to determine if the coil were there or not. 

The circuit could be turned on periodically to determine if there was a device there and go into high power mode. 

Another way the detection of a coil could happen is by monitoring the phase of the current and voltage phase, the receiving coil would change the relationship between them, this is how it is done on some wireless power IC's.

You don't have to do this with a microprocessor, you could use a 555 timer for the pulse to check the circuit, after you did so you could 'and' the result together with the current detection signal, if it's high then keep the power active, if it's low, then shut the circuit down.