Actually, the consideration is the other way around...

Are you likely to have a voltage, spikes or other undesirables on your incomming line likely to damage your PIC? The PIC is unlikely to be set to OUTPUT (unless you explicitly do it) since Microchip put some effort into ensuring the PIC initialises at Power-ON into Input (High-Impedence) mode. Because if it DOES initialise as OUTPUT, will it be HIGH or LOW? Then that negates the common practice of tying unused pins to VDD or GROUND.

You are now intoducing a new problem - Since the INPUT ADC Impedance is around 10K, putting such a high (10K) Resistor in series as per your suggestion is going to seriously affect your ADC readings and deviate them from what is true and expected.

I wouldn't worry about the PICs inputs becoming outputs (unless you are deliberately including a self-destruct routine into your PIC) as much as potentially what you are likely to be feeding the PIC.