When Shadar mentions that as his Soul Mate, Oliver has reincarnated several times. This is the game's in-universe explanation of coming back to life after losing a battle!
Also in a flashback, Oliver remembers his mother and the Mr. Drippy doll, with her talking in a funny voice that Drippy and the Fairyground fairies normally use. She assures him that all fairies talk like that. Makes more sense in that Allie isn't Alicia's soul mate, she's the same person, and she's familiar with the fairies of her world talking funny.
Oliver and Phil, age 13, dream of building and designing cars, and live in 1950s Detroit, even if its going by its nickname instead of real name. So, assuming best case scenario of 1950, this means that if they want to build cars, they'll be entering the workforce in 1955, after high school; if they want to design, it'll be in 1959 after college. Detroit started collapsing like a landslide pretty much starting with the 1967 riots, and the American auto industry began to collapse soon thereafter with competition from Japan and the oil crisis. If they end up building cars, thats twelve years of prosperity before an always-increasing tremendous chance of layoffs and no solution, forever. If they end up designing cars, that's eight years before things get significantly worse, although its more likely to be a dissatisfying job life, worsening income, and forced to leave their hometown and friends than layoffs. Have a happy future, kids! Remember, follow your dreams and never give up on them!
Manna. Remember that the souls in each world are connected. When the White Witch starts dropping manna and turning the people of the entire Other World into ravenous, bloodthirsty, mindless creatures, how did that translate into OUR world?
Kublah's soul mate is a dog, and the dog's owner (a jock) is the soul mate of Tengri the dragon. Never mind the fact of how animals and humans can share a soul, but dogs live only a fraction of human lives. If what happens to one soul is linked to the other, than is Kublah, already a middle aged man, predestined to die within ten years, while Tengri dies within a generation of human years instead of thousands?
Not necessarily, just look at Oliver and Shadar. As long as Kublah is alive, his soul mate will continue to reincarnate (not always as a dog). Thus, presumably, in this system, reincarnation pairs remain in circulation, just being reborn the usual way, unless by some improbable coincidence they die at the same time.