That's not what the police are saying
I don't know whether Heath was guilty or not but I wouldn't necessarily trust what the police say. There are many cases where they have been "120% certain" that someone committed a crime but were wrong. And in this case, given the amount they have spent on the investigation and the high profile they gave it initially, it would be embarrassing if they had to say the allegations were false.
Why would people make up stuff about some Ines who's died
All kinds of reasons. They may want attention, they may be hoping to receive compensation, they may be mistaken as to the identity of their abuser (as happened with Lord Alpine, although he was alive at the time) and so on.
I agree that we should start by believing someone who alleges they were a victim of child abuse. Too often in the past they were disbelieved, allowing abusers to continue their activities. However, that does not mean we should continue to believe blindly. Their allegations may fit our preconceptions but that does not mean they are true. They must be investigated properly, which is not always easy when the accused is dead.