I would unlace the wheel, loosening the spokes gradually, going around the wheel multiple times until there's zero tension, and then take them off. Then set the rim down on a flat surface and see how warped it is. If the worst spot is no more than than 4-5 mm off, you can probably have the wheel rebuilt (or do it yourself). If it's worse than that, you'll have nothing but problems. If you do rebuild, use all new spokes.