Much the same sentiment as above - if you have rocket igniters connected to pins on the micro, you really need pull-downs - of about 1K - on them anyway.
Arguably, you should have each of them passing through a NOR gate, the second input of which is (in common) driven by a separate output pin through an inverter, requiring both a high and low output from the micro simultaneously to actuate the igniters.
dc42:
For detecting unconnected output pins, you could ... build pulldown resistors (e.g. 1K) into your rocket igniters, or use some other mechanism so ensure that it takes more than a few µA to trigger them.