Well after those long and nice episodes with that fine ship, it was pretty sad, but sometimes I felt it was a funny reaction from those Klingons who did not even find out for themselves what the countdown was.I was 16, saw it on opening day, and remember that night remarkably well. Still have the movie promo booklet I bought that night. I wasn't too upset; I knew even at that age that all the talk at the time about "taking Star Trek in a new direction" on the part of Harve Bennett, etc. was all BS and that Spock would be back in the next movie.
I recall being much more bummed out when the Enterprise was destroyed in Star Trek III.