Well I tried this in a blank dummy lot with a dummy Sim (you only need one because this 'Group Talk' thing seems to be a self-referential interaction). I used boolprop to spawn the Memory Manager, adding the '*Talk->Cory's Group Talk' to the Sim's pie menu. Put an FFS Degugger box on the lot, clicked on it and chose 'Force Errors...->On Off-world'.... Nothing.
I turned boolprop back on and repeated and got about 5 or 6 Object Error dialogues. I deleted the one referring to "Memory Manager - Old" and reset the others. Sure enough when I clicked on my Sim her pie menu was without the '*Talk' group, so it can be done.
I opened up the lot I'm having trouble with and tried the process there. There must have been a thousand Error dialogues - it's a medium-large lot. I was cancelling some and resetting others; I came across an instance of "Memory Manager - Old" and deleted it; I think I came across another but reset it instead of deleting it by mistake. When the process was over the '*Talk' group was still in my Sims' pie menus.
I had a vision of floating through space as a Sim and gazing down on a big, fiery ball. So I exited the lot without saving. I think I'm going to go with the wussy-but-safe move-out-and-back-in method.