They don't die in the packets (tomites, cysts), they must be vacuumed out. If the temp is too low, they will reproduce in the cysts and become free swimming, infecting your fish. The free swimming stage is also the only time that meds can effect them. It's a question of achieving balance, and you know your fish better than i.
As far as your question regarding meds, if your fish are tolerating them well and you are uncomfortable not using them, then keep using them. If you want to try an alternate method, then discontinue them and use temp + daily water changes. It would not hurt to combine these methods. Keep in mind that the meds themselves could be stressing your sensitive fish, and that sometimes ich infests the gills invisible to you, so it may be that all these times you thought it was gone, it was really still there but hiding behind their gill covers. IMO salt is not effective, but it may reduce stress in species that naturally have some salt in their water and have an indirect effect.