Brock has been in the show since the very start, and seeing him leave is like seeing Ash leave in a sense. He's become a character that so many viewers are used to seeing. Even though he doesn't do much like other characters have, he's an original character and to see him go from the show possibly gives me mixed feelings about it.
For one, other than him being in the anime for a long time now, he just gives it some of its personal humor with the ladies and now Croagunk always being behind him because of it. He's also changed throughout the anime, meaning he's grown some. He's become more knowledgeable and has given the show a father figure for Ash and the third party member.
With him being gone though, it leaves room for someone new with a new inspiring goal other than the obvious second traveler female. Plus, Brock doesn't do much in the anime now these days and well unlike before him being gone makes it feel like you won't even miss him. Although, it's still mixed as it all depends on what new dreams Brock has in mind and whether or not that could possibly give him a boost in the show if he stays.
In short though, I'm a little in the middle of him leaving the show or not. We'll see...