Regrettably, I must (for now) take back what I said.
I didn't realize that after voicemail was enabled for Group Ring, Architect will no longer take the Failure path when the call fails to reach an agent. Instead you hear a message that voicemail is not configured for the group, and then the call disconnects without a return to Architect functionality.
A developer just submitted an SCR, IONEDGE-4206, to change that behavior, but you will need to contact Support and request that enhancement to get your needs added to the SCR. Otherwise, Product Management will not see a need to change it, since the system is currently behaving as designed.