Nope, they abandoned it because the language design was unsound, and in retrospective a GC was a critical missing piece.

"Alef appeared in the first and second editions of Plan 9, but was abandoned during development of the third edition.[1][2] Rob Pike later explained Alef's demise by pointing to its lack of automatic memory management, despite Pike's and other people's urging Winterbottom to add garbage collection to the language;[3] also, in a February 2000 slideshow, Pike noted: "…although Alef was a fruitful language, it proved too difficult to maintain a variant language across multiple architectures, so we took what we learned from it and built the thread library for C."

https://en.wikipedia.org/wiki/Alef_(programming_language)

"Problem: with C's memory model in a concurrent world, hard to know when to free items.

All the other languages in this talk are garbage-collected, which is essential to easy concurrent programming"

http://go-lang.cat-v.org/talks/slides/emerging-languages-cam..., slide 19