Let penetrating oil work a few days. Vises or pipe wrenches do more damage than good. With the wheel removed, straddle the fork blades around an open wooden stair tread. Work the handlebars back and forth with your body weight. You can apply a great deal of pressure this way - easily enough to bend the fork. As long as it's steel, you can bend it back. See Dave Mouton's web page for how frame builders re-bend & true forks with a piece of chain and a 2x4.