IMO, a restyling alone should not classify as a separate car entry. A different hybrid schema should. Thus, if you look at the differences between Prius I and Prius II, I think that classifies as 'different car', especially since 'Yota made changes to the hybrid system that warranted them *renaming* it (?)
3rd-gen (3.5 ? 4th-gen ?) IMA, as long as the workings are similar (electric motor, battery pack, no propulsion w/o ICE) should stay in the existing HCH category (denoting model year, of course). This includes reworkings to the ICE itself, unless it's something major that Honda doesn't normally do (like, Atkinson-izing the engine, for example), including an engine family change - but as long as it's an Otto-cycle engine, that keeps it in it's existing class.
Just my opinion, others' are welcome to chime in. And I'm looking forward to this car as well - I may actually replace the HAH with one
To address the original topic - there's a chance. Expect 8th-gen Civic sales to be fairly brisk - people have been sitting on their hands for almost 2 years now for the new Civic. What helps is that the delta between 'listed' and 'real-world' mileage seems to be less for the Hondas than for the Prius. What hinders is that the Prius outsells the HCH by a substantial margin (but, then, this could be a help for the HCH, as well). In any case, it'll take time - look at all of us new HAH owners just now coming into our own, most of us not having owned hybrids before, and having to learn how to get the best out of the car. So you may actually see the avg *drop*, before rising
While the 8th-gen Civic will be released for September, something tells me the new HCH won't be sold for a month or two after that ? Just a feeling I have, nothing to substantiate it.