My memory on these things is actually not as good as some people who remember everything. I have to look things up these days, but I know where to look.
The HII should expire at Final 6 in keeping with other recent F3 seasons such as Nicaragua, HvV, Samoa, and Gabon. There was no idol in play at the end of Micronesia, as Parvati chose not to look for the one that got rehidden.
The HII has evolved since it was introduced as a full game element in PEI (S12). I tend to look at the more recent as indicative of the rules, as in S12-14 they were still on a learning curve.
We never did find out about the rule for Tocantins, because it never came up as the HII was not played the whole game, but Sugar played hers at F6, Russell at F6, Sandra at F6, Chase and Sash at F6.
Which brings me to ... Jeff said to someone in his blog or answering a question or in a tweet (clearly I forget where), that Rob can use his in the Final Episode. That would be the second F5. Unless Jeff meant, UP TO the final episode, which is the first F5. It sounds like they changed the rules this season <insert your own snark>.
They never showed us the scroll with the rules. So I would be expecting F6 were it not that Jeff said that.
It appears that the idol will be in play when the returnee comes back in the game, which I find completely WRONG in that the returnee has had no shot at finding an idol. I suppose it would be nice if the returnee had been voted out idol in pocket, nice for him or her. But really, why protect someone who let that happen?