How can I check if an IO pin is dead?
As per your comment that you're bit-banging the I2C: are you totally sure that nothing else changes when you change your I2C setup to that pin? Can you use a multimeter to check the resistance to ground/supply/other outputs (with it off)? It could be as simple as physically moving wires around is causing an issue. 

Your other options are limited without a scope. You could buy another dev kit to compare with, having two anyway is sometimes useful! 

If you haven't done so already, it might be prudent to add some protection to the SDA/SCL lines. Series resistors (if you are unsure how to determine then 300R would be a good start) and TVS diodes can make quite robust protection against ESD and accidentally shorting the lines to power rails.