They didn't "take ownership" the range is vested with APNIC labs (check the whois record) they route it with permission and share data.
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.
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].
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.