When the two new control towers were opened in 1993-1995, the old tower was relegated to a ground control center during the day. At night, the old tower was used as the sole functioning control tower. I'm not sure if they still use this setup today.
The new Hyatt at Terminal D will be a Grand Hyatt - decidedly more upmarket than the present hotel. To the best of my knowledge, the existing Hyatt at Terminal C will remain in operation.
The existing ramp control towers at each of the terminal are being replaced (the SkyLink people mover tracks have obsucred their views) by new towers attached to the SkyLink stations. The new people mover has really changed the way DFW
looks - it's astounding.