In the beginning of episode 1 of Digimon Tri, we see glimpses of the second generation Digi-destined (Davis, Yolei, Cody, and Ken; sorry I only know their English dubbed names) being destroyed by what looks like Alphamon.
Several (in universe) days have past since this event, so why has nobody inquired about what happened to them? I would imagine that they would be missing and somebody would notice.
Are the 2nd gen Digi-destined even alive after their defeat?
Disclaimer: This Q&A is about an ongoing series as of the time of the posting, and future episodes may reveal more on the subject or change the perceptions shown here.
Around a decade has passed since the defeat of MaloMyotismon and the restauration of the digi-world. The show did not yet disclose what happened to the 2nd generation digi-destined. It might be that they lost contact with the 1st gen, moved away, or any other explanation.
In our real world a decade is time enough to make even closest friends drift apart, more so when they are children, bound to move along with their parents when these parents change jobs or get transferred.
But I would hold my hat on that issue. It is very unlikely that Koushiro "Izzy" Izumi would allow digi-destined to not stay in touch. They even have a social network of sorts "Digi-destined of the World", that they use to warn the other digi-destined of the infected digimon returning to Earth.
So, their apparent disappeareance is more likely to be a plot device, to be revealed in future episodes. It is not like they don't care or are not in touch, it just wasn't shown on screen yet.
During the first Tri movie, it's mentioned that it had been a year since the close of the digital gate, and that it had not opened since. If anyone remembers during Adventure 02, the premise was that the loss of the Destiny stones caused the digital world to merge, but BlackWarGreymon sealed the gate.
It's at this point that time becomes alternate for Digimon Tri. Rather than the dark spires reappearing, Himekawa is trying to get her digipartner back, much the same way that Oikawa had lost his partner. She sent Ken, Youli, Davis, and Cody back to the digital world, but they lost to Alphamon. As in dead, both they and their digital partners.
This is why Himekawa is aware that these kids are 'offline' as shown in the computer screen. She purposefully infected Meicoomon with the dark power that Ken as the Digital Emperor had used in the form of control bands. The assumption is that she figured if she corrupted the digital world, it would force a reset to create homeostasis between the digital and real world. But she also has to deal with the original DigiDestined.
The other possibility is that Himekawa intended to get her partner back by recreating a digital partner, but instead got Meicoomon who wasn't a perfect digital creation, hence the infection, figured out that she would have to force a reboot and began eliminating the DigiDestined, starting with Ken, Davis, Youli, and Cody, and it was in fact Meicoomon who killed the kids.
