...after reading the prologue and epilogue?
I don't remember exactly how I felt, but I know I was really confused. I had missed book 46 since my bookstore didn't have it, and it was the only time I'd missed an Animorphs book like that. And the whole plot was starting to change in every book, so there were a number of details I was confused about. At first I was wondering if I had missed something, then I realized that the death hadn't happened yet, of course.
As the last few books were coming out, I sort of forgot about the impending death, possibly due to my hoping that it wouldn't really happen. Then came 54, and I saw the inside cover with the conversation with the Ellimist again...it was sad.
The line about the strand of space-time going dark and coiling into nothingness was really depressing and hard to take in.