With 6 weeks of "Fallow" (no fish time) you can be about 80-90% sure your tank is safe. While the tank has no fish, I would turn the temperature of the tank up to about 84-85 degrees. This will speed up the life cycle of the Ich. There is new research that Ich can live, "unhatched" for up to three months.
It kind of sucks, I know... but 1) your corals, if you keep any, will LOVE the down time and the increased temps, 2) the Micro life like the pods and the micro starfish will LOVE the down time, nothing to eat them. You will have more life going on in that tank and some pretty cool stuff to watch till you get fish back in there.