Hello there! Before you proceed any further, and if you have not yet finished reading Bethphel's Diary all the way to the end, ask yourself if you're willing to risk spoiling the surprise. For what follows will reveal much of where the novel is going. Indeed, for we're talking about a sequel.
You have been warned... If you're still with me, let's go. Hold a deep breath, and scroll away! 
So, Bethphel is dead. No resurrection in my books, not even if the body didn't disintegrate as any "proper" Bhaalspawn would. Her son, Ben-Oni was rescued and nurtured in a manner not unlike the one Irenicus was using in his lab for those creatures in the glass jars. When it was safe for him to leave his temporary artificial womb, he was adopted by Imoen (as you can see from the epilogue). Wait... you may ask me. Imoen as an adopted mother? Wait and see... I'm not telling everything, you know. 
What I'm gonna tell you, though, is this. The sequel will be based on the game of Baldur's Gate II: Shadows of Amn, with the Throne of Bhaal expansion. The main protagonist, however, will be Ben-Oni. Yes, he is not a child of Bhaal, but rather a grandchild. Still, that fact could interest Irenicus by itself. More so, considering the manner in which he was born.
At the time of the events in the game, I'm considering to have Ben at the age of fourteen years. Still a child, but already half an adult. I'm planning to cast him as a Transmuter Mage dualed into Thief. Why? Simple, really. You know that the BG2 characters start at a considerably advanced level. But Ben-Oni is not supposed to have any real experience. By dual-classing him into a Thief right away from the start (or rather, after having released Minsc and Jaheira, which should raise him to level 9 as a mage), I will effectively create a novice thief, too weak to do much and be in constant need of protection, yet still with enough hitpoints not to die on every step.
As well, I cannot see a teenager as a high-level fighter, or a wizened archmage of 20+ level or something, etc. A thief, specializing in traps and trap detection, sneaky enough to go through the most narrow of places where no adult have ever gone before, is what I have in mind for Ben-Oni. And when he recovers his magic abilities, I will choose an appropriate pivotal place in the story, making it look as if he acquired some special abilities because of whatever events transpired thereon.
Oh, I should take care to get him a familiar before turning him into a thief. He's gonna be Chaotic Good, and a cute little fairy dragon should prove a great "imaginary friend" that no adult believes in. What else? Low strength and constitution, but exceptional intelligence and dexterity. With his magical side, he should still be able to take on the Planar Sphere as a stronghold quest.
But why Transmuter (the school of Alteration), of all specialities? Think of his "special abilities" as a kids magic. They make things happen simply be believing in them. Altering reality. And that is why I will limit his arsenal of spells only to transmutation and illusion spells. The latter taught to him by Jan. Oh, the gnome should prove a fantastic "chaperon," indeed!
An interesting alternative is to make Ben-Oni a Wild Mage, instead of Transmuter/Thief. However, I don't know much about that class yet, and how it plays out in the game. But I'll keep it in mind...
And now... welcome Rita! A half-drow, daughter of Viconia and Edwin, no less. Thirteen years, only a year younger than Ben, but "just the perfect age for a drow," in her own words. A mischievous daredevil, equally proficient in the arts of stealth and that of a dagger virtuoso. She has spent many years perfecting the art of sneaking away in the crowd without having her half-drow identity noticed. Yet she knows when to laugh the enemy in the face, and does so with a flair. A tomboy of sorts, always having to rescue Ben-Oni's butt from the tight situations in which he constantly puts himself. Picking on him, of course, but always with a smile. In other words, a female Swashbuckler (love the concept, by the way! a-gallant-man-rescue-damsel-in-distress placed on its head). Chaotic Neutral. Triple stars in dual daggers.
Possibly, I'll make the story last over a few years, so that our heroes could grow just the right bit older and truly fall in love between themselves. But that remains to be seen. The rest of the characters are certainly still not too old for a brawl. And what about Boo, you may ask? Either the miniature giant space hamster have truly a giant lifespan, or else we're talking multiple generations of Boo's offsprings. When marching together, 'tis truly a force to be reckoned with!
But hey, here is some more food for thought. Remember Tamoko was pregnant from Sarevok at the end of Bethphel's Diary? Guess whom I'm gonna cast as her son...
Ah, if only I could give Ben-Oni and Rita some custom special abilities, instead of those thrown in by the game when you create the main character! And while Viconia's portrait from the original game of Baldur's Gate should do just fine for Rita, I'm lacking Ben's portrait still.
As always, your opinions and suggestions are welcome and treasured. Feel free to drop them into my guestbook or into my mailbox.