Well you’ll have to make some choice like for every other type of game. The server only have to send what player B can see instead of the whole game at every turn so it’s should reduce bandwidth until late game. Also if someone lag it’s only affect him instead of every players in the lockstep model. In the end I guess you’ll have to put some code that let everyone know if someone lag really bad so everyone will be aware of that, especially the player who is lagging.
On the blog he say they are aiming 40 players with 1mbps so if you go with a more reasonable amount of players like 8 we typically see in RTS the bandwidth should not be too high.
In your exemple the bunker will be destroyed for everyone since it’s destroyed on the server, as for player B one way would be to put the game on fast forward as soon as he receive the update until he get in sync with everyone else, something similar to what you see in shooter games when lagging a bit too much.