Did you actually bother to look at a data sheet for any of the devices you are talking about?

The inputs of all MAX232 devices (at least authentic ones), are internally pulled low,
so that when left floating, their respective output is high, which is the serial idle state.
The RS232 inputs can also be left disconnected, and live inputs can be plugged in before the chip is powered.

Not bad what two minutes of research can uncover.

Similarly with Pics, you can turn on weak internal pull-ups and leave their inputs floating as well.