Blockquote If it is dead, is there anything I can do in the future to prevent this (besides being more careful)?
One thing I have experienced in my short time working with the Raspberry Pi is that you should always make breadboard changes with the Pi powered down, double-check to make sure you don't have cross-connections, then power up. Though I'll admit that can be frustrating and time-consuming, especially when the change is a very quick one.