I can see the more gentler Rand making a deal with Fortuona but Egwene attacking the Black Tower? Sorry I can't see that. Both rebel and Tower Aes Sedai wanted to remove the Black Tower but they had come to realise that even if the Tower was reunited there were too many Asha'man and they were too well trained for any assault on them to be guaranteed to win.

If I'm not mistake one sister though that even if the gathered in all the Aes Sedai any assault on the Black Tower would probably see have the Aes Sedai dead.

Those are not casualties Egwene would be prepared to suffer with the Last Battle around the corner. Not to mention it would seriously piss off Rand who she wants to get on side.

If the White Tower was to learn about a battle at the Black Tower between Asha'man then they might seize a chance but the Aes Sedai are not organised as a military group. If they find out of a battle it would take time for Egwene to gather enough sisters to strike. Given the way the Asha'man do business once the shooting starts it will be very violent but also very quick. I would be surprised if the fighting were to last a day and by the time the Aes Sedai showed up the battle would probably be over.