1. If APP control were overload, they will immediately give adjacent frequency (center control). If they do, you can contact center control or continue flying on your own. (Squawking VFR / 1200)
I assume you mean
after you leave the Class B/C airspace? Two-way radio communication is required to be within either class of airspace, so they can't give you a frequency change while you're still inside the airspace... if they are that overloaded, they would have held you on the ground (or outside of the airspace) until they can accept you.
2. Normal hand-off. "Contact center control on xxx.x for traffic advisory, good day"
Just a note: sometimes this transfer from Approach to Center (or vice versa) can be coordinated ahead of time such that an actual radar handoff is performed; in this case, you wouldn't hear "radar services terminated" at all and would be handed off just like an IFR aircraft.
1. "Continue flying on your own (squawking 1200)". As we know we are still in Bravo airspace, how come they leave us "flying on my own with squawk 1200"..??
I don't think this would typically be done. Even if you request to terminate radar services while you're inside a Bravo, it likely won't happen. It often makes things much easier for ATC to have you squawking a discrete code, especially if there is other VFR traffic in the vicinity.
Instead, you can probably expect to be vectored out of the Bravo first or simply told to remain on the discrete beacon code until you exit the Bravo on your own.
2. As we know that Bravo airspace has bottom & top ceilling. How if I climb to above B airspace (but below A airspace) and request radar service termination..?? Has anyone have experience with this (VFR)..??
If you're in Class E/G airspace, you can always opt out of radar services you may have previously been receiving. If your intention is to climb out of Bravo airspace and terminate the radar services, you might want to mention that in advance (either on the ground or with Approach - whoever you first contacted to get the beacon code). If the radar controller knows that is your intention, (s)he will likely terminate the services for you in the same transmission they inform you that you're leaving the Bravo airspace (as well as approving a frequency change).
3. How if I want to descent above B airspace until below bravo airspace (just passing B airspace vertically)..?? Of course I need to hear the magic words "clear into bravo airspace, squawk xxxx". Then, after I fly below B airspace, could I request radar service termination..??
Minor nitpick... you technically shouldn't ever hear "cleared into" if the controller is using by-the-book phraseology - it'd be "cleared to enter," "cleared out of", or "cleared through" (see FAA JO 7110.65 ยง 7-9-2(a)). Similarly as above, clearly communicating your intentions with the controller will likely make the termination automatic. In other words, the controller will use the "through" clearance since you're merely transitioning through the Bravo for some (relatively) short period of time and will likely terminate your radar services when informing you that you're leaving the Bravo (i.e. descending below it).
4. For point number 2. Could I still request flight following..?? (above B airspace) What the advantage for pilot to having it..??
Of course (dependent on factors like controller workload, of course). You'd have the same advantages as it would provide while in any other type of airspace.
