I can give you an answer of sufficient specificity to my own standards regarding the Hittites, I could give you a rough 'guess' for the Thracian half of the question but that wouldn't really do.

The term 'Hittite' as normally used tends to cover two different but related things; the first covers a specific ethnic group tied to the city known as Nesha or Kanesh, who would come to encompass the region named Hatti, based around the city of Hattusa and formerly controlled by a people modern scholars term 'Hattians'. The Hittites called their own language Neshili, and whilst it's often referred to as 'Hittite' by many modern linguists some prefer to call it Neshite or Nesite for that reason. The second covers anyone who was a subject of the Kingdom formed by the Hittites. That not only covers those who spoke Neshili, but Hurrians, Luwians, and a number of other peoples with their own distinct languages and heritage. Ideally I'd like a better differentiation between these two concepts, but part of the reason why they are often used interchangeably is due to all of these cultures merging together to a certain extent, particularly during the Hittite New Kingdom era.

By the end of the Hittite New Kingdom there were already declining numbers of Hittite/Neshite speakers, which is observable in the Hittite textual corpus we have access to. We see an increased presence of Luwian names and of the Luwian language. So by the 13th century Neshite is already losing ground to Luwian. Then the Hittite New Kingdom breaks apart like an egg. It's not the end of the story for people identifying as Hittites though- there's an absence of textual evidence for large chunks of the former Hittite territories for many centuries afterwards, but there is an exception in a group of states termed the Neo-Hittite kingdoms.

The Neo-Hittite kingdoms seem to have formed shortly after the collapse of Hittite central authority. They were primarily based out of the city of Carchemish, in the south-east of the New Kingdom's territories. It's believed, but not proven, that originally there was just one large Neo-Hittite state that splintered and fragmented into the patchwork of Neo-Hittite states visible not long afterwards, and in Assyrian records. The Neo-Hittite kingdoms all seem to have been Luwian speaking, with almost no visible use of Neshite at all. What's rather telling is that they continued to refer to their land as Hatti, and other neighbouring peoples continued to do so as well.

There would still have been Neo-Hittite states during the 7th century BC. However, most of them by that time had long since been swallowed up by the Neo-Assyrian Empire, and seem to have been rather extensively settled in that era. The last Luwian inscriptions come from the period in which the last Neo-Hittite rulers are replaced by direct Assyrian governors. We see no more direct evidence of Luwian speakers in the region after that, so far as I'm aware, nor are we aware of anyone identifying as Hittites in that region by the time the next big state comes to rule the area. So it's generally assumed that whatever Hittites were left in the Neo-Hittite states disappeared sometime during the 7th century BC.