Some pilots offshore switch to DG mode after landing, and then switch back after takeoff. Depending on the platform and how long you're there, your heading indicator can be pulled off, sometimes by much more than 45 degrees. It's a tradeoff - switch to DG and not have it pulled off, and then forget to switch it back and have it drift off over time, or leave it in slaved mode, and reslave it after takeoff. I tend to just leave it slaved, because it's hard to know how much it will be affected, and assume it will be off after takeoff. The PNF just calls out track from the GPS, and reslaves the compass once we get stabilized on a course. It's a PITA to have no idea which way you're going, especially in the dark, other than reading the track from the GPS, but we deal with it the best way we can.