That’s not how inbreeding works.
Remember that likely every human on the planet (with the exception of some tribes men or possibly some native Americans) is a descendant of Genghis Khan.
Assuming magic is passed down through bullshit genetics like fanus traits are (It only takes one parent and always breeds true, with neither squibs or muggle-borns like an actual dominant or recessive trait.) humanity could be remagiced within a millennium.
If it’s the other way around though, and it only passes with both parents being magic, and therefore Ozma and Salem need to actually Adam and Eve it, I.E. a gene pool of 2, then you’re probably fucked by inbreeding issues.
Your best bet would probably be to aggressively eugenics as much diversity as possible and minimizing the expression and propagation of the various inbreeding recessive traits they would be plagued with. There would also be the problem of needing to gradually genocide away humanity2.0, as they are incapable of contributing to your magiced human gene-pool and therefore definitionally superfluous, despite outnumbering you by millions.>>104518718>Only in the simpler lifeforms. Humans are way too complicated for that. Two directly inbred generations is the limit for a human.
Again not how genetics and inbreeding work. Genetic bottle necks are bad, but given a long enough time natural selection and new mutations can straighten the gene pool out.
For example scientists currently believe that the entirety of new-world monkeys are directly descended from a population of around 50 or less monkeys which managed to raft across the ocean for several weeks on a giant chunk of ground and trees swept away in a giant storm. (Which is a once in a million years type of event)(This is literally the only plausible explanation for how the americas got monkeys when they did.)
Also you can totally get away with direct inbreeding for longer than that, look up perigee-collapse or Cleopatra’s family tree.