basically, this is what i've learned from having ich, and talking with dmed.
the heat does not necessarily kill the ich. hwat it does is simply speed up its lifespan. the ich, initially will get worse after increasting the temperature (becuase it speeds the process). This causes the ich to go to the floor of the tank, where it will multiply like mad. it is in this short window of time that the salt kicks in to kill the ich.
the fish are however susceptible to other diseases afterwards, so you should watch carefully afterwards. do water changes regularly, also, replace any water with new salt. after this is done, stop with the salt. lower the temp a couple of degrees each day back to the status quo, and boom bam. there you go.