So if sora gives ventus his heart shouldn't sora loose the ability to use synch blade? I know he will still be able to wield one beacuse that one he earned form riku in KH1 but as for the other I don't know. Unless he uses eraqus keyblade which I don't think would happen most likely.

 

So wait but if sora gives back ventus's heart roxas will like sorta disappear because when sora became a heartless it released ventus's heart and that's why roxas looks like ventus and upon the power of sora  roxas himself can dual wield due to sora and ventus hearts and xion is also sora so thats why she as well has the kingdom key 

or maybe roxas's apperance will change?

Edited March 3, 20169 yr by ExcisionGaming

so, keyblade transformations come to mind when it comes to a synchblade like abillity, since different keychains have different transformations, why cant there be a keybalde that splits into two? ventus had his keyblade split into six energy swords in bbs for wing blade, some thing like this could happen, and since it could level up more and more, it could start as two then level to max into who knows how many blades? 

Considering the manga's  canon and references in term of what should have been of the serie we can conclude that:
1- A keyblade choose his master and won't change his aparences until a final "aspect" (Like the keyblades of Terra,Aqua and Ventus in the beginning of the game);
2- The keyblade is connected to one heart wich means that people "connected" to the heart have influences in the keyblade.

We can probably conclude other things but for now that will do.
In KH 358/2 days (Roxas and "Organization XIII" story) we see that:
1- Roxas manipulate Sora keyblade;
2- Xion created by the Organization absorb Roxas power being finally able to use and call a keyblade.
3- After betraying the Organization and running away (for Xion) Roxas have to fight his friend(*)
4-After defeating Xion, Roxas regain the powers Xion was absorbing from him.

5- Wanting to realize Xion last wish Roxas depart to liberate Kingdom Hearts, it's at this point that Roxas is shown to be able to dual-wield.(*)
6- He then meet and fight Riku(*).

Ok that was ~ the game. Now the manga (will only go to the * points):
1*- Roxas battle against Saix (it happens in the game too) but he fight him when as his lowest being completely overwhelmed by Saix powers, but he retaliate giving his all in one last attack, it's in this attack that his keyblade for the first time of the manga (and serie??) change in appearance(<- will come back to this). Roxas keyblade will stay like that until the end of the manga. He even fight Xion with that keyblade.
2*- Roxas call upon his second keyblade again diferent from the keyblade you can see (in the manga) at this point you can suppose it's Xion keyblade and it emerged from the Power and Feelings Roxas felt when Xion disapeared.
3*- When touching Roxas keyblade Riku , who had lost Xion memories, remember her, renforcing the origins of that keyblade, but Riku don't fight with it giving it back to Roxas and ... loose and transform in Ransem.

Well, there is some diferences between game and manga. For the game, being able to change our Keyblade was something needed and obvious but since in the manga the keyblade don't change well we can think a little.
Concerning dual-wielding and taking as basis what was said up there: 
I think Roxas will maintain his dual-wielding, first because the 2 keyblades are a part of him representing his "hope" and "sadness".  I don't think it's a good comparison(? Sorry for this ) but think of it as "What kind of keyblade Ventus and Vanitas (if they had persisted as one single entity) would have been able to obtain".

Roxas is a simily born without memories but throught a lot of experiments he gained memories, feelings and his own heart. Influenced by his desires and feelings he created his own keyblade ("light") to gain the power to create his path but devasted by the lost of his dear lover friend a conflicting emotion appeared in his heart creating a second keyblade ("darkness").

So for me Sora will lost his abilty to call Ventus heart when waking him up but will maintain the dual-wielding ability until the reapearance of Roxas. 

PS: Sorry for that text and all the errors in it. I did my best but  my english is ... bad.
      Most of the text is probably out of context and completely erroned and if that's the case please tell me, by mp the incorrect parts or where i could get more                   apropriate information for it. Thanks a lot.