Seasons in which we have finished below halfway in the second tier and not been relegated:
1977-8: 12th (22 clubs at the time)
1984-5: 18th
1999-2000: 16th
2001-2: 13th
2025-6: 13th
All of our other bottom half finishes in the 2nd tier (1979, 1988, 2011) and our sole bottom half finish in the 3rd tier (1981) resulted in relegation.
I am not old enough to remember 1977-8.
We started well in 1984-5 but this turned out to be a false dawn (we got 8 points from 4 games, but 3 of the teams we played were relegated). We struggled most of the season but we were saved by Glenn Cockerill, Mel Eves and the poor quality of the 3 relegated teams (Notts County, Wolves, Cardiff) and Boro who finished 19th. Most memorable moment was either beating Leeds when their cro-magnon fans caused trouble, or the Unexploded Bomb game.
In 1999-2000 Warnock bailed us out of the mess Heath had created with some good work in the transfer market and getting better performances out of some people who were already there. We had a run of 15 games or so where we were very good and once safety was secured the team tossed it off for the last 9 games and didn't win any of them. We beat WBA 6-0 which was pretty memorable, and of course who can forget the Port Vale game.
We never really got going in 2001-2. We drew the first 5 games and were off the pace throughout. Defence was decent but goals were a big problem. Most memorable moment by a mile was the battle of Bramall Lane. After that we were close to the relegation pack but a couple of good wins saw us safe easily.
This season has some similarities with 1999-2000. beating the Pigs home and away is the standout highlight surely: I will always remember relegating them.
We also had pretty boring top half seasons in 2000-1 and 2009-10 where playoff challenges faded away pretty early and there were few highlights, though we beat Wednesday in both seasons. 1998-9 similar although we had the Arsenal void cup game. 1982-3 and 2015-6 in the third tier - both 11th place finishes - were more frustrating than boring in my eyes.