ICH wont live without fish.. it will get to the last stage of life and then die... if the newly hatched parasite cant find a fish in 24hrs they die off.... but the issue is the heater.... danios are extremely hardy fish... they can live in water that fluctuates allot and is in general unhelty...... its not a matter of getting a heater if you keep fragile fish.... it about getting a heater if you want to keep any tropicals...... BTW if theres no fish in the tank ATM you will need to cycle it agan... keep the danios in the tank and go get a heater/ thermometer and monitor your temps for a few days till you get the heater dialed in......
also i have to add... it probably wasn't the ICH that killed the fish.... it was more likely the stress form ICH and temp swings..... Ive had fish sick with ICH for a month strait and didnt lose one... it seemed like nothing wold cure it till i did research and learned about the life cycle of ICH..... the reason it never went away is because as soon as the white spots where gone i wold treat for 3 days and then stop (like i was told here and like the box said) what the box didn't say was that you need a temp of 82f to get the life cycle of ICH down to 3 days..... that in turn gets the parasite to the point in its life where the meads are affective.... now when i see ICH i can usually have it gone within a weeks time..... you really should google "ICH life cycle" or something to that affect and see for your sell.... if what Ive typed isn't making sense, other websites will........