Magus had come to realize that Thanos is a bigger threat to his plans than he tought and decides to attack him, Warlock, Gamora and Pip with his army of demons. Fighting against seemingly impossible odds Thanos convinces Warlock to use his Soul Gem to defeat the opposing army. Thereafter Thanos sends Warlock, joined by Pip, through a time-probe to destroy the Kismet Trail, a sort of trail of potential destiny, leading to Warlock becoming Magus.
Meanwhile Thanos reveals to Magus that his reason for aiding Warlock was the fact that Magus might one day oppose him in bringing Death to every world.
As the two engage in battle Warlock, still on the Kismet Trail, encounters the In-Betweener who has been sent to force Warlock to metamorph into Magus. The In-Betweener tells Warlock that although it might not seem like it now but one day Magus will be the champion of Life, created to defeat the champion of Death - Thanos. Warlock, standing at the crossroads of fate, rejects the notion of Magus being a potential force of good and decides to destroy the line of his own destiny that would eventually turn him into Magus. As Warlock destroys his destiny Magus fades out of existance
As the timeline where Warlock turns into Magus ceases to exist the only people aware of the change are those closest to the proverbial eye of the storm and as Warlock and Pip celebrates the destruction of Magus and The Universal Church Of Truth, Thanos stands triumphant having erased a future champion of Life from reality