"Může se stát cokoli!" should be accepted - reported.
Added. You were not the first one to report.
Is it usual for cokoli to be the last word in a phrase?
It can certainly be anywhere (especially in other sentences), including at the beginning. The last position is good for it since we often want to stress it (really anything!)
Cokoli se stat muze-- does that work?
yes, but requires quite a special intonation