Infinite will bring a slight boom back to the forum, but there likely won't be any long term traffic. There's a few reasons why the forum has slowly but surely trickled out to the point it is today.
First, normal entropy. The story of Halo has been significantly discussed already, and though the amount of games have nearly doubled since the site's glory days the amount of lore has not. This isn't because 343i has failed in any way, it's simply because that's how stories are.
Second, the community part of the forum has become fragmented. This is partly natural, but has worsened because of things that have drawn people away. Namely, Skype and Discord. During my time as Site Mod, the subject of off site chat was brought up and I carefully constructed a couple of chats in Skype that could allow quick conversation between staff members and moderators. I declined to create an official non-staff chat in Skype because I knew it would draw people away from the shoutbox, which is more important to the site than I think anyone else realized. It's pretty simple, when people are in the shoutbox talking to each other, they are on the site. If they are on the site, they can see when someone replies to a topic they have an interest in and post a response. Posts are the lifeblood of any forum, community forums especially. Just before I retired a freshly promoted community moderate approached me with an idea that he had to create a Discord for the forum. I told him it was a bad idea but didn't clarify exactly why, so that's my bad.
The worst period of inactivity that had occurred before Discord was between Halo Reach and Halo 4. Even then, there was at least two or three posts per week and half a dozen members on at all hours of the day. The longest inactivity in the shoutbox was less than three hours. As I type this, I am literally the only person logged onto the site and one of only 14 that have been on today. The most recent topic posted on this forum was yesterday, but the one before that was over a month ago. The shoutbox contains shouts from January 16th, which are from 343iBot welcoming new members. The Discord currently has 30 people online, none of which are on the site.
New members gravitate toward the topics they are interested in first, then the shoutbox once they've posted. There they make new friends and decide to stick around. However, with a discord they have to go through extra steps to talk to anyone and then they have to keep it open. If it's their first time using discord, the whole ordeal becomes a confusing mess and they quickly give up.
So, will Halo: Infinite reignite 343iCF? No. Not as long as the 343iCF discord exists. Not as long as the more active members are drawn away from the site where they will have difficulty meeting new members and welcoming them to the community. Get rid of the "official" Discord and maybe.
tl;dr this is my biggest "I told you so" ever and the Discord created discord with our amount of people online.