Voltage isolation at IC pin when Vcc=0V
Add another Schottky diode from the non-inverting input to the positive power supply rail. The Schottky diode will be reverse-biased in normal operation, but when the power is off it will conduct any spikes to the positive rail where the bypass capacitors will kill it off, and even if the user pumps it the zener will prevent the supply rail from going too high. 

Since Schottky diodes have lower forward drop than regular diodes, almost all the current will go through the Schottky diode. You can use a single BAT54S dual diode to replace both D1 and the new diode. 

Right now you have a 1N4148 for the negative side, which is not a Schottky and significant current will flow through the IC when the input goes negative, which could lead to latch-up and thence destruction of the IC.