This depends on how you have your swap configured, you can continue to safely use your 770 as a flash drive as long as you partition things intelligently. See the instructions for extending your root filesystem for the "best practice" in setting up swap and lots of other stuff.

If you fail to partition properly, you may not crash the 770 immediately but you can see erratic behavior up to and including crashes. As to what happened in your particular case, you'd need to examine the state of the kernel from a memory dump to know for sure... or partition your 770 safely and sleep soundly knowing that it won't be an issue again.

Mike