Detroit and the south side of Chicago are probably the most obvious examples of what happens when more brown (or black) people start moving in large numbers. Beautiful neighborhoods and homes destroyed over decades. At some point, white-flight will no longer be the answer.
It never should have been an answer in the first place.
"White-flight" is in reality a first world luxury for those with a lot of resources to waste and spare who just dont want to go through the energy and effort to protect their territory. This unfortunately sets a bad precedent to those who wish white people harm.
White people since the 60s have been slowly losing place as the alphas of society. Think of the hippie and feminist movements, to Hollywood doing trial runs with Black and Asian actors changing to more aggressive, dominant, main character roles and whites starting to take a backseat, to nonwhites starting to get seats in political positions, to the now glorification of modern day black american culture (rap, hip hop, and hoodrat mentality). All of this has had a disastrous effect on old time white culture, the average white men's masculinity and place in society, as well as white women's perception on society.
Despite societal and cultural changes, work ethic for whites hasnt changed for the most part, still earning their place as great students reliable employees, and average to above average earnings in pay. Higher pay gives you the luxury of living in nicer areas away from crime and dangerous day to day living. This unfortunately made most people soft, gave a warped sense of reality, and caused aggression instincts to atrophy. Since easily accessible internet and transportation has been available this really is no longer an excuse but the multigenerational effect of comfort os hard to shake off. Just look at college students from the last 10 years and see just how delusional to reality they are. Effects of family generations living in suburbia and modern brainwashing.
Going back to white flight, one of the two most basic rules of warfare is to never leave weapons or resources for the enemy to use and never leave open territory for the enemy to conquer and claim. Fleeing a city or state leaves it vulnerable to possesion by foreign entities, expanding their territory and losing yours. Eventually there is nowhere to flee. And this is one of the end goals of the enemy because you'll be easy to pick off at that point.
What will you or your family do then?