Player B would have no say in the matter. This is because Player B has "left the alliance". Here's where things get a bit confusing, but consider it like this:
1) Players A & B found Nova Alliance
2) Player B "leaves" the alliance.
He flips his Alliance Marker to the -3VP side. He is now no longer a member of the alliance; he keeps his own score, cannot travel through any other player's territory or share in their attacks, and is generally autonomous again.
3) Player B still technically has a Nova Alliance Marker (which is now flipped because he left), and therefore can never enter into or form another alliance, nor can he rejoin the Nova Alliance. This is true because no player may have more than one Alliance Marker, and there is no way to remove an Alliance Marker once you've accepted one.
4) Player A is allowed to freely invite another player to the Nova Alliance so long as (A) there are unclaimed Nova Alliance Markers, and (B) there are at least 6 players in the game. Once all Nova Alliance Markers are accepted by players, whether or not any of them are active, no additional players may join that alliance.
Conceptually, think of Player B's overturned Alliance Marker as a bit of a blacklisting. It is a mark that he must wear to inform all other societies that his people are oathbreakers. That is why he cannot get rid of it or ever join/rejoin an alliance once he leaves one.
1) Players A & B found Nova Alliance
2) Player B "leaves" the alliance.
He flips his Alliance Marker to the -3VP side. He is now no longer a member of the alliance; he keeps his own score, cannot travel through any other player's territory or share in their attacks, and is generally autonomous again.
3) Player B still technically has a Nova Alliance Marker (which is now flipped because he left), and therefore can never enter into or form another alliance, nor can he rejoin the Nova Alliance. This is true because no player may have more than one Alliance Marker, and there is no way to remove an Alliance Marker once you've accepted one.
4) Player A is allowed to freely invite another player to the Nova Alliance so long as (A) there are unclaimed Nova Alliance Markers, and (B) there are at least 6 players in the game. Once all Nova Alliance Markers are accepted by players, whether or not any of them are active, no additional players may join that alliance.
Conceptually, think of Player B's overturned Alliance Marker as a bit of a blacklisting. It is a mark that he must wear to inform all other societies that his people are oathbreakers. That is why he cannot get rid of it or ever join/rejoin an alliance once he leaves one.