I think we see much the same role for Mez in 2013. Perhaps even reduced if Chapman wants Hannigan. OTOH, I can see where Hannigan is given Chapman and Arroyo while the stable pitchers like Cueto, Latos and Bailey start learning to work really well with Mez.
2 things happen in 2014, Arroyo's a FA and Hanigan is up for arb one last time. 2013 is an awfully important year to bridge to Mez if that's what will be long term.