If shorted in Strong Drive mode, the pin will be blown up. You may check the state of the pin on the PSoC power up - if it shows 5V, it is blown up. (Normal state on startup is LOW).
I blew up few pins configured in Strong Drive mode by loading high frequency output to a ~0.1u capacitor. All of those pins turn HIGH on the power up. I haven't seen damaged pins which are stayed LOW.
Do not overdrive pins, the rating is 4mA (source) / 8mA (sink), and for special pins 4mA (source) / 25mA (sink). So for 3-5V, loading resistor should be >1k.