I am not as familiar with the K-12 system, as it's changed a lot since I went through it, but my college students seem to have gone through school with no deadlines and the ability to resubmit any and all work any time they want, with the expectation that they'll get at least 50% just for turning in the assignment (even without their name, lol). So while year-round school with absences whenever might be compatible with this system, it's not particularly compatible with a functioning educational system where the class is being taught as a unit and are more or less learning the same things at the same time.

Additionally, it only works if teachers are completely exchangeable, and are also allowed to take time off whenever. What is likely to actually happen is that teachers will be paid the same but expected to be on call year-round (they're already expected to be on call 24/7 during the year in a lot of places) with no breaks and limited ability to take even sick leave. I'm fully in support of year-round school - I think it's a great idea for a lot of reasons - but I would caution that this type of implementation might be a bit harder to pull off.

IMO, at least, education happens when there's an actual interpersonal relationship between the teacher and the class, as well as between members of the class. This doesn't happen with the app-driven schooling my nephews are completing, where everyone is in a different place and they just follow lessons on a computer all day with teachers as facilitators and not actual instructors. It's why we see massive declines in student motivation - they've lost the relationships that tend to motivate us as humans, and that's a really hard thing to get back. My best classes have been when there are meaningful relationships between me and students, but also between students in the class, and we are all tackling a problem/topic together. There's something about shared suffering, you know?