In my experience, the reincarnate buff on the boss will show 100% of the time now even if it fails (only lands by casting it on a close proximity, gotta “hug” the boss before casting it)… The fail rate is like 90% (and it is shown in the chat when the resurrect buff is not working). It it’s a successful buff, there will be no message whatsoever in the chat, only the reincarnate buff.
When the boss is successfully reincarnated, we get 4 / 6 cubes(nontoken / token); and 6 / 9 cubes (non-token / token) total if the double attribute procs (only if the boss is successfully killed in time too).