Do you think we’ll ever learn more about Maester Wyllis?

[James Steller]

In case you need the reminder, Maester Wyllis is a minor character from TWOIAF. He writes a thorough account of Hardhome while living there under a wildling’s protection. When said wildling is killed, Wyllis has to flee for his life. He returns to Oldtown and finishes his book, but then disappears. He is last seen looking for a ship to take him to Eastwatch by the Sea. 
Much as it raises a lot of questions for me, I can’t help but feel like we won’t get any answers.

[Curled Finger]

Maybe indirectly if Davos or another character actually gets there OR Sam could come across the book itself.  Martin is decent that way, dropping a morsel on your plate to chew on and forget then toss another on after you've long forgotten about it.  Wyllis seemed to have focused his study on Wildling healers, which just happens to be a thing that may come in really handy at the Wall and in Hardhome just now.  Could be we run into such a healer.  Could be such a healer understands greyscale or perhaps maybe what befell Coldhands.  Could be these healers understand skinchanging far better than anyone else?  Could be Uncle Benjen is with a healer or was...   Ah James, this could be a lot of fun, Man!  

[Jon Fossoway]

No need to hear from him anymore. A very small anecdote with a closure. Here in south America happened quite a lot, when catholic missionaries (around the time spanishfolk start building stuff in here) got very attached with the natives. This trope repeats itself in books, movies et al.

[GZ Bloodraven]

4 hours ago, James Steller said:

In case you need the reminder, Maester Wyllis is a minor character from TWOIAF. He writes a thorough account of Hardhome while living there under a wildling’s protection. When said wildling is killed, Wyllis has to flee for his life. He returns to Oldtown and finishes his book, but then disappears. He is last seen looking for a ship to take him to Eastwatch by the Sea. 
Much as it raises a lot of questions for me, I can’t help but feel like we won’t get any answers.

2 hours ago, Curled Finger said:

Martin is decent that way, dropping a morsel on your plate to chew on and forget then toss another on after you've long forgotten about it.

This is one of those Tolkienian "impression of depth" things that is so vital to keep any fictional world vivid and alive. The main events obviously have to be engaging, and George will have probably 5 years of intense description, about 30 years of concrete but loose description, 130 years of condensed description, hopefully another 130 years of condensed description with some intense but singular description from Dunk and Egg, and then the world book and various allusions fill in 8000 years of this vague "here's an unexplained anecdote for fun" that is required for the "casual mentions" part of the impression of depth. I don't think we will see any more of this, much like many of the random tidbit mysteries won't be solved. There may be Hardhome descended wildlings who claim descent from Wyllis that we have yet to see, or his ship may have crashed on Skagos and some Skagosi claim descent, or maybe his ancestor were taken by the Skagosi in that post-Hardhome cannibal theory, or maybe he never made it north and we'll discover a shipwreck. Those are the only ways I see Wyllis becoming relevant again: for what it's worth, I think he made it back to Hardhome, and his line died in the blaze six centuries ago.