Add (attach) your progress view to the main window of the application instead of a subview of the controller or view that is being removed when you transition.
A - use KVC
id appDelegate = [UIApplication sharedApplication].delegate;
UIWindow *keyWindow = [appDelegate valueForKey:@"window"];
B - use keywindow property of UIApplication
UIWindow *keyWindow = [[UIApplication sharedApplication] keyWindow];
This property holds the UIWindow object that is most recently sent the makeKeyAndVisible message.
C - use windows property of UIApplication
UIWindow *keyWindow = [[UIApplication sharedApplication] windows].lastObject;
Suggestion: just tag your progress view so you can easily find it later when you need to remove it.
UPDATE:
Now that you have the main window (the top most view in the hierarchy), you can add any type of stack object you like (a view, label, activity indicator, etc.) just like you would to any UIView
.
// Easiest and most readable way to get the key window
UIWindow *keyWindow = [UIApplication sharedApplication].keyWindow;
UIView *testview = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
testview.backgroundColor = [UIColor redColor];
[keyWindow addSubview:testview];
testview.center = keyWindow.center;
UPDATE 2:
As a last resort if you are navigating in ways outside of traditional UIViewController
transitions and presentations, you can always add a new window to the stack as seen here in this SO post.
If the issue of the disappearing view persists you might want to try changing the way in which you navigate through your views / controllers OR pass references between the controllers to allow this "disappearing" view to live on.
Another reference regarding this type of navigation.