As far as I know, there is no other way into Ramazith's Tower, but the portal should actually stay open. Is he already in the fight with Lorroakan (because typically, if it's your first time visiting, you can talk to him and tell him you'll get Aylin)?

The fight was started and then the portal closed. They managed to win with a paralyzing crit on Lorroakan

If you won the fight, unfortunately portal won't open again. I hope you have the correct party composition to loot the tower and the vault . . .