The consensus guess is that Brett Favre will return. But Favre has proved it's virtually impossible to predict what he'll do next. The Vikings, although they won't say it, need to know Favre's plans before March 5, when the trading deadline opens, so they would be able to compete with other teams to acquire, for instance, a Donovan McNabb from Philadelphia or a Matt Hasselbeck from Seattle, or whomever they would try to bring in. Source: St. Paul Pioneer Press
If the Vikings give him an ultimatium there's no doubt he'll retire then return. No one dictates what Jesus Favre does.