In one of those janken tournament vids, Mariko seemed really laid back when she lost. She was genuinely happy for Sumire.
This makes me wonder how she views her role in AKB48. She obviously enjoys it a lot, but she doesn't seem to care a lot about making senbatsu and stuff. Maybe she thinks she had a good run and it's time to let the newbs take over?
If she graduates, I think she'll go the MaiMai route, except maybe less TV and more modeling. I highly doubt she'll move to SDN.