Gale never gave a book to Walt. The handwriting in the book and in Gale's notebook are not the same. It is obviously Gretchen giving a gift to Walt. However, it just so happens to set Hank off into thinking Walt may be his Heisenberg...so, he'll be trying to nab Walt next season...and Walt, who is out of it at this point, will somehow get back into it...perhaps due to his hubris or perhaps out of need...either way, he'll get back into it and I guess Hank will either bust him or confront him...and he'll end up in New Hampshire.
I think Walt will somehow enlist Saul's "eraser" to get a new identity and then just goes on the run.