Pier B is actually staying, though it will be so extensively refurbished that the final version will be unrecognisable from the Pier B we are all familiar with at present. However, Pier C is going because its location prevents two-way traffic flow on taxiways through to T2.
As some have pointed out, there may be a case for MAG constructing some additional remote aircraft parking stands aside from the terminals redevelopment plan. I don't know what the costings are for this type of work, but they should be affordable based on traffic projections going forward.