Probably ten times the population of the Sanctuaries are scattered across the continent in subjugated population, but the population loss is quite rapid.
Tieflings don't exist in a traditional sense, but if you wanted to include a bloodline particularly touched by Hell's influence, I suppose it would depend on which end of things you're asking about. The Sanctuaries would likely view such people highly suspiciously and the pre-war cultures might also have prohibitions punishing tieflings.