They will never be forced out of the high end niche. They made >50% of the phone markets revenue in the past year. But global phone sales are going down as prices go up and people already have phones. And with that pattern, their even higher margin services business will have a cap.
Also, Apple, unlike Dell, would be able to control both the Intel and Windows part of cheap phones. They could use their older chips and contract TSMCs old fabs for a much cheaper price. They could develop their own OS based on iOS but maybe more like Android so most of the apps would be similar but it would still have an inferior experience.
Also, they would be able to target the European and Americans users who currently buy cheaper Android phones. They have the money to buy services, but not to spend over a grand on a phone. That itself is hundreds of millions of people.
I just hope the only major American phone manufacturer doesnt become irrelevent on a global scale.