Keep AI the way it is for now...
As for offline, I see 1 pro scenario & 1 pro scenario, but still requires server connection.
Make Story Mode Offline, but update to your server profile upon online connection. With checking info & time accrued, have safeties in place to catch when someone is offline for a week supposedly, but has 3000000 more steel; or was seen as offline with the relative mats you could accrue in that time, but shows duplicate actions on the same account for that same time period. Story mode can have little affect on online play, we just have to make sure no one is exploiting it with hacks.
Keeping it P2P, could the software be managed so in a LAN environment, whether a cafe or party at home, if you are playing with only people in the LAN your bandwidth is used for brief communications from the server, but the actual gameplay of the match stays within the LAN connection?