How to reset MCP2200 to default settings?
I think you're out of luck on this one. If the configuration memory was erased and the app crashed before the new values were written, it would explain why it's no longer enumerating - the firmware doesn't read valid config data and can't recover.

(Interesting side note: the MCP2200 is a relabelled PIC18F14K50 with pre-blown firmware inside it. You may be able to salvage it for other uses - the FOSS replacement for the MCP2200 firmware doesn't appear to be ready yet.)