You're ignoring the basic psychology and economics of business. A few things:
a.) workers are currently far more productive than they're paid for, and this will remain true even in the face of the DNC's most radical wage policy.
b.) products currently selling at $400 won't sell at $4,000. People just won't buy them, so a firm would never set the price that high. Instead, they'd cope with increased labor costs by allocating resources from things like executive pay.
c.) even if liberal economics result in mass offshoring and loss of jobs, things won't be so bad. Because if this takes place, the US will be eliminated as a consumer nation, which will force workers and the government to begin collectivized domestic production. If the government doesn't act, however, there'll probably be violence, with worker uprisings, confrontations with police, another phase of Occupy, and leftist groups using the anger to increase their membership.