Name Magic Pantheon Plane Zereth Greater Powers Lesser Powers Death Necromantic Pantheon of Death Shadowlands Zereth Mortis Eternal Ones Undead Disorder Fel Unknown Twisting Nether Unnamed Unknown Demons Life Nature Pantheon of Life[23] Realms of Life[24] Unnamed Unknown Wild Gods Light Holy Unknown Unnamed plane Unnamed Unknown Naaru Order Arcane Pantheon of Order Unnamed plane Zereth Ordus[25] Titans Keepers Void Shadow Unknown Unnamed plane Unnamed Void lords Old Gods
https://warcraft.wiki.gg/wiki/Magic#The_cosmic_forces
Plane of Death
If a being of Death is killed on the mortal plane, their essence returns to the Shadowlands to be reformed, similar to how demons reform in the Twisting Nether.[13] However, if such a being—either the soul of a former mortal or a native being of the Shadowlands—is destroyed in the Shadowlands, they die permanently and their soul is lost forever.
https://warcraft.wiki.gg/wiki/Shadowlands#Inhabitants
Plane of Disorder
Since their spirits are tethered to the Nether, it is the only place where demons can truly die.[15][16] As such, when they are killed, their souls are calmly sent back here, where they await for some time to be reborn in new bodies, with all the knowledge of their previous lives.[17]
https://warcraft.wiki.gg/wiki/Twisting_Nether
Plane of Life
When Wild Gods die, they go to Ardenweald in the Shadowlands and enter a wildseed to be taken care of by the caretakers and tenders of the groves of one of the celestial trees until they are ready to be reborn through the Grove of Awakening,[21] and can later return to the Emerald Dream.
https://warcraft.wiki.gg/wiki/Emerald_Dream
Dimensius will unquestionably return.
Regardless of whether his imprisonment in the Dark Heart will lead to some kind of death, unless he’s specifically slain in the plane of Void, I doubt it’s a character that will or can die.
If we posit that all six cosmic forces more or less behave the same and are more or less equal beyond their respective characteristics, we have seen at least half of the six planes—the plane of Death, Disorder and Life—displaying the same characteristic in terms of the cycle of death and rebirth for beings originating from these planes.
There’s thus no reason to suspect or believe that this isn’t true for every plane.
Dimensius being, as you put it “reborn”, is arguably a matter of when not if.