(SPOILERS) Xykon's next move should be...

[Callista]

...grabbing Roy's body and reanimating it or destroying it.

Logically, Xykon should know that the Order is the one thing standing between him and the Azure City gate right now.

Whether he understands that the Order is the worst threat he faces, and whether he knows that Roy is the leader the others depend on, is still up in the air.

However, the ideal best move at this point is to demoralize his enemy by removing their leader--Roy--for good (barring True Rez). Striking against Hinjo would have been more devastating to Azure City; but he already knows his hobgoblins can take the paladins and their army--so the OotS is the obstacle he doesn't yet have a firm plan to defeat.

However, Xykon has a history of underestimating his opponents--meaning he may not even think of the importance of a leader to a group like the Order; or, if he does, may not think that one fighter more or less is important enough to bother with, since he is already a great deal more powerful than the Order with or without Roy.

We'll just have to see if he's smart enough to realize the power of morale...

[Bel_Bel]

I think Xykon is going to the keep and making an attack their like he originally planned to.

[factotum]

I doubt Xykon knows any such thing. He just defeated Roy without a great deal of effort, and he probably doesn't even remember the rest of the OotS, much less consider them a threat. Also, the hundred or so paladins guarding the throne room are likely to make up more of a threat than the members of the Order, even though they'll be lower level, simply because of their numbers.