Barnabas is in control. He has bitten Maggie, so she is compliant to his wishes. Maggie has shown her father that she has no fear of Barnabas, so when people start wondering who did something to Maggie, Sam will know it couldn't have been Barnabas. And Sam has been given the task of filling in some details on the portrait of Barnabas while Barnabas himself goes and feeds on Maggie again. Nothing can stop Barnabas now!
Unless...perhaps...[spoiler]Josette influences Sam to paint fangs on the portrait of Barnabas.[/spoiler]
Note: Yes, I know, the spoilerized idea didn't actually happen. But If I unspoilerize it, then innocent, vulnerable newbies (come on, Johnny Depp fans!) will know for sure that it didn't happen. We can't have that.