As of now it's really all up in the air. If BioWare has the Warden pull a Fiona, then no more Warden title. Personally I find the latter preferable to becoming some sort of long-lived quasi-ghoul like Avernus.
I aggree completely, but Avernus never aimed to remove the taint from his blood, he thinks the taint is a gift Grey Wardens couldn't use properly. He says so far Grey Wardens just used this gift for trivial matters like sensing Darkspawn and taint has a great untapped power in it. So, The Warden wouldn't become a ghoul or taint wouldn't be removed from his/her blood.
Actually, if the Warden finds a cure that would stop the spreading of the taint in is blood, that wouldn't just turn him into ghoul or make him live long. Avernus wasn't ghoulish, he just lived long thanks to blood magic and he avoided the calling for a very long time and even this would be more than enough to avoid a calling for a lifetime. But his true aim was to change the Joining ritual so that it will not spread in Grey Wardens' body and grant Grey Wardens much more than just sensing Darkspawn and Archdemons.
According to Avernus, Grey Warden blood has a great untapped power and using this gift just to sense Darkspawn was foolish. He summoned demons with blood magic but some demons were more familiar with blood magic than humans (since demons taught humans the blood magic) so he couldn't control all the demons. But, Avernus says, they are not familiar with the power of the taint so they cannot counter it.
In DAO, if the Warden drinks the Avernus' Concoction, it grants him/her new Grey Warden abilities. I'm curious what kind of powers would the taint grant to him if he can unlock this power. I'd love to see that.