Regarding FCC licenses, it appears that Augusta-Richmond County is licensed for frequencies now used by existing Palmetto 800 sites in Augusta, McBean and Blythe. Because those licenses belong to Augusta-Richmond County (they are a consolidated city/county govt entity), they can be used for whatever system they choose, within the limits of the license. Therefore, it would seem logical to me that, rather than establish new licenses for the new system they would endeavor to make use their existing licenses currently used by Palmetto 800.
A simulcast system seems likely for the same reasons that simulcast is popular in so many other urban locations across the country - it minimizes the number of frequencies required to be licensed and allows wide area coverage. It's possible that the FCC would let them amend their existing licenses and allow them to transition from one system with separate sites to a new simulcast system.
A transition from an older system is typically a gradual process, with individual groups of radios (ie, a department or two) switching over in a staged fashion. They'll likely peel frequencies off of the existing Palmetto 800 sites as more and more radio traffic is moved to the new system.
A P25 Phase II system allows 2 talk paths per frequency. This means they double the number of available radio channels for every existing frequency they have now. So, there are many potential options they can choose from in how they design the new system reusing what they have.
There's no guarantee this is what will happen, and I have no knowledge of this specific situation - meaning this post is mostly speculation.
