Well I just took the time to re-read all the title page stories more intensively and I´ve made a strange observation. All protagonists of the title page stories seem to have something in common and that´s that they most likely will all reapear in the final stages of the main story. Let me explain why I think so.
1st Step: Let me begin with the guys who became Marine characters in the Title Page Stories, which would be Coby/Helmeppo and Jango/Fullbody (Hina´s boys).
Well I think there were already enough speculations among us fans about seeing Coby at the end so I think that this doesn´t require more elaboration. However Jango and Fullbody weren´t elaborated so far. The reason why I think that we will see them again is not because of themselves but because of who their commander is, Captain Hina of the Marine HQ. I for one consider as close second after Smoker when it gets to the Marine´s captains. Many of us are sure that we will see Smoker at the final arc, me too. But I finally began to think that Hina will be there too.
Maybe it is just be but she was Smokers class mate at the academy and therefore I think that Oda could pull a "we went through so many things together" with these two characters too.
Plus I find their names rather interesting, "Smoker the White Hunter" and "Hina the Black Cage". Hmm, Black&White…coincidence?
Just let us hold the idea for the moment it that Coby, Helmeppo, Jango and Fullbody will be there either when Luffy becomes Pirate King or when he gets arrested. It mustn´t be them who do it, but let them be just there.
2nd Step: The characters who are still pirates after the Title Stories, The Buggy Pirates, Alvida and Ace.
Well though I don´t see Buggy as powerful enough to mess with the great pirates his history with Shanks and Whitebeard just makes me think that he will also be there if all these great powers should collide (Pirate´s Summit anyone?). I´m not saying that he will be able to beat anyone but having him just there would somehow work. And if Buggy is there then Alvida would also be there and just like with Coby it would so much be Oda style to have the characters from the first arc included in the final one.
And that Ace will reapear at the finale (Pirates Summit) is out of question I think. Same goes actually for Blackbeard IMO but that´s another story.
So let us think for one moment that Ace, Buggy and Alvida will be there. Well one thing is clear Luffy will become the next Pirate King, which means that none of them can be it. But just as it was the case with the Marine characters, they would be there to whitness it.
3rd Step: The character´s who became Business Men in the Title Page Stories, Hatchan, Wapol and Gedatsu.
Well they´ve all become successful and famous business men. Ok we didn´t see Hatchan become successful and famous but I think the fact that he found that legendary souce will make him as famous as Zef is thanks to the Baratie.
Ok if we would interpret all of them as successful and famous business men then I think it is fair to assume that they will travel a lot around in the One Piece world, or to be more precise they will get invitations to big and exclusive events.
NO! I´m not thinking that they will be invited to the "Pirates Summit". But there´s a certain event where I can see a lot of prominent faces reapearing and that would be Luffy´s exection after he became Pirate King (if he gets executed that is).
If Luffy should really get executed at the end of One Piece then this would be the perfect event to showcase all of the Title Page characters at the same time. Lets think of it, if Coby, Helmeppo, Jango and Fullbody should really be around when Luffy gets either Pirate King or arrested, then it is very likely that they will be among the Marine officers that will whitness the execution.
And if Buggy and Alvida were chasing Luffy for so long they will certainly even come to his execution (digsuised of course). And Ace as Luffy´s brother is also a must (also disguised).
Well and the business men Hatchan, Wapol and Gedatsu will probably all have VIP seats for such an event.
Well this is actually the conclusion of all what I wrote up. I think that all the Title Page characters will be there to see Luffy as the next Pirate King (who gets executed).
I know some of you will say that it is likely that we would see even more characters reapear if such an event should happen, however not all would be plausible (Dorry and Brogy or Enel for example). And all of the Title Page character´s would already have explenations on how they could make it that far while others for others there would always be the question on "how did they come that far?" or "why haven´t they been captured?", Kuro and Krieg could be such examples.
Anyways it was just a brainstorming I had while I re-read the title page stories and I thought I should share it with you guys.