I don't think so. Iirc, the one who lost his ability only saw some yokai so his connection with them wasn't very strong to begin with. And Natori's mentor also lost his ability likely due to age (just my hypothesis since they say children are more likely to see yokai since it's folklore that they're aren't fully human yet. But then grow out of seeing them eventually) his power was also only low-mid ranged. Natsume is quite stronger (even if he doesn't know how to use it) so I think it's less likely he'll be unable to see yokai. It's never been mentioned or shown that those with strong power lose them over time.
I think the main reason we only see Reiko in her high school years is bc she died young (which I'm curious about. Like how exactly??) But the rest of her time probably involves Natsume's grandfather and that's purposely left an even bigger mystery for us to agonize over.
I kind of agree with you about Natsume's strong power
So I really hope he can keep that even though he's old
And yes, Natsume's grandpa really intrigued me
Especially in the chapter twin dragon,
After that ch, I really want to know about his grandpa
Is he an exorcist? Or some kind of youkai?
But sometimes I thought it is sensei
HAHAHAHAHAHHAHAHAHAH
Reiko die coz of sum youkai i think?
SENSEI?!! ahfhfjs I can't (ノ≧∇≦)ノ someone make this lore immediately!
As in previous ch, there's someone who lost the ability to see youkai after they become an adult
Did Reiko becomes like that too??
That's why there's only a highschool version of reiko in youkai's memories
And will natsume become like that too?
I'm scared of the future