Following HR’s death in The Flash, he reverted to the incarnation of season 2 and Harry, in season 4. This tradition continued until season 6, which featured a great Harrison Wells spin through Crisis on Infinite Earths.

With the destruction of the multiverse, The Flash was left alone with Nash, until the situation was found to be far more complicated than that: untold numbers of Harrison Wells survived the Crisis by merging into Nash’s consciousness.

This included Reverse-Flash, but The Flash was able to exorcise it from Nash’s body. The rest, however, still exists in his mind and could presumably be used in future episodes.

One particular version of the character, HR, may play a role in the next episode of The Flash and the season as a whole. The season 7 premiere episode is titled “All Right Wells Finish,” which is also the title of one of HR’s books.

If so, he could interact heavily with Nash as one of Harrison Wells’s “ghosts,” or perhaps he could play a much larger role. A post-Crisis HR could even be Harrison Wells from The Flash.

That doesn’t seem too far-fetched, as one of the first episodes of the season is when The Flash brings a new Wells. Also, reusing an existing version would be unprecedented as noted above.