Given the number of people now relying on Clouflare 1.1.1.1 to "get Internet" (ie using 1.1.1.1 as recursive name server), I can't imagine APNIC deciding to stop Clouflare using this range.
It seems "too late" to revert this decision. Otherwise people will experience "Internet stopped working", blaming their ISP.
APNIC may decide to keep a working DNS server on 1.1.1.1, but ethically, routing traffic to someone else than Cloudflare is not great.
If just temporary assigned to Cloudflare, APNIC shouldn't care if it sees a better use for the range. Supporting unintended uses only encourages various types of abuse. And changing DNS settings is easy enough.
That said, if a lot of people rely on 1.1.1.1 as DNS, it's worth considering whether reassignment qualifies as 'better' use of this resource. Not to mention the hassle caused by making changes to popular [anything].
Fixed IP addresses change and are deprecated all the time. It's of zero concern to APNIC that customers of Cloudflare or various ISPs can no longer access the internet because they relied on a temporary IP assignment, after the service was gracefully terminated and deprecated, with ample lead time.
That being said, the use by Cloudflare is an excellent way to reclaim this part of the IP space, I don't see why they would terminate this collaboration.
It seems "too late" to revert this decision. Otherwise people will experience "Internet stopped working", blaming their ISP.
APNIC may decide to keep a working DNS server on 1.1.1.1, but ethically, routing traffic to someone else than Cloudflare is not great.