We have nothing to fear from a "hijacked convention". Whatever comes out of the convention must still be ratified by the states.
Bring on ConCon!
Sure, half of the country wouldn't accept its validity, and there would be a Civil War.
Actually, that's the plot of my third novel.
Here is a long excerpt, giving a fictional take on the dire aftermath of a runaway ConCon.
http://www.enemiesforeignanddomestic.com/FESP.htm