Unmarked spoilers.

The only problem is, we don't know how many keyblades there are. In Kingdom Hearts there were three: Sora's, Riku's (which was destroyed when Sora used it, or maybe it just disappeared) and Mickey's.

In Deep Dive alone, there are four: the three that the dual-wielding Unknown has, the Oathkeeper, Oblivion (which was thrown to Riku) and a Kingdom Key that he took out after throwing the Oblivion to Riku. Then in the end you see Mickey flip down onto the roof wielding his Kingdom Key. As far as we know, none of those people are Sora, so that leaves out his keyblade, which would mean that there are five keyblades.