Generally speaking, Legends books (or other media) are not canon under the Disney canon policy unless they are explicitly referenced in new media. Thus unless some book makes explicit references to the Bounty Hunter Wars books, they aren't canon.
You asked specifically about the Guild and Boba Fett's fate. There hasn't been much of anything about the Bounty Hunters Guild (or the bounty hunters themselves) in the new canon, so we don't know anything about what happened there. Nor do we know if Boba Fett survived the Sarlacc pit. His StarWars.com databank entry summarizes pretty much all of his Disney canon appearances, but is rather vague about what happens to him after he falls into the pit.
Things get a little murkier when you look at interviews though. Jonathan Rinzler, author and editor for Lucas Licensing's book division, stated the following in a 2014 Reddit Ask Me Anything:
Q: Jonathan, In your mind, does Boba Fett Escape the Sarlacc Pit?
A: Yes, he does. I have been in meetings with George where he confirms that Fett survived. If it comes from George then it’s true!
Make of that what you will.