You should try reading the manga. It's really interesting! Even the current arc. Personally, I really like the time skip. I think the story will be boring if sensei continues with highschool. Because the formula will be the same: training camp, new school rival, matches, national, etc. For me, this arc gives something more refreshing.
As for spoiler: they went to national, win against Nekoma, but lost in quarter final. Then the 3rd years graduating. Then time skipped to Hinata, already graduated, go to Brazil to learn beach volleyball. Stories about them in 2nd and 3rd year only a 1 chapter flash back.
Okay... tbh, I picked this up 2 days after a haitus of reading Haikyuu, starting from chapter 100 smth. This took a whole different turn than I thought lol. I thought the series would've continued on to their second year. Lol, guesss not. Also that scene where Hinata broke out in tears got me