I don't think anything is known about Banor's end. There are some in-game references to Banor such as the prayers in this book and this book.
Further references to Banor include stories from the Kha'labal Chronicles and the Creation of Humans series.
Considering the praise that Banor gets throughout the books and other in-game references, it seems that Tibians consider him to be a God, and he may have ascended from being a human to being a God. Here's an example from Shauna, an NPC in Carlin's prison:
Shauna: I worship Banor of course.
Shauna: For me, he's the god of justice.
Another example can be found in the book The Soulvortex:
Its said that in ancient times, the gods created a great vortex to allow the souls of spirits from 'beyond' enter the realm of Tibia. Through this vortexportal many great heroes were able to manifest themselves on Tibia. In their new bodys they fought againt the forces of destruction. But also agents of destruction and evil entered the world through this portal. More and more the dark forces used the portal to spread over Tibia and to annoy, disrupt and subvert the brave people of the world. Some of the evil spirits remained long enough in this world to wreak even more havoc on the good people of Tibia. Destruction of all that others had built, slaying of new manifested souls as soon as they left the vortex.
The gods watched in grief what had become of their great accomplishment. And one day Uman and Banor combined their awesome forces and split the vortex.One strand now aimed to the isle of rookgaard, the other one remained aimed on the temple of Thais.
From this day on the newborn heroes awakened on the holy and protected isle of rookgaard and only the stronger and better prepared souls could travel to the continent.
Guided by omens an expedition of brave warriors from the thaian order of the knights of noodles traveled the perillious seas the the remote isle of rookgaardand discovered the new soulvortex.
Soon this base was built and this fine academy founded.
Praise the gods and our King.
Thorwulf even straight out says that he's a god:
Thorwulf: Some strange warrior god from the south. Seeing what kind of warriors those people are that god is not doing an impressive job if you ask me.
Lugri, however, says Banor is not a god at all:
Lugri: Banor isn't a god at all, but one of their tools. It is stupidity to worship a tool, isn't it?
None of it tells us how Banor met his end, but at least we know he is not forgotten, and may be watching over us all as we go into battle!