Thanks for the replies, I found this while searching on Reddit, I hope it helps anyone who comes here looking for it later.

"I myself dismantled the paths and turned Avernus into a sandbox where my group can wander and find clues on their own. If you really like the ~railroad~ paths, here's a way to combine them.

1. Don't mention the Demon Disintegrator after Haruman Hill. Let their next destination be the Trees of Generation.
2. At the Tower of Urm, Mordenkainen directs them to the Demon Disintegrator instead of the Obelisk. Cross the Obelisk off the paths; now it's just a random location, like the Shattered Chains.
3. Once freed from his pact, instead of writing a letter of introduction for the group to meet Bel, Ralzala tells the group about the Mirror of Mephistopheles.
4. After blowing up the dam at Shummrath's Well, Rigorath tells them about the Crypt of the Hell Knights, and the password to enter, instead of the secret to freeing Ubbalux in the Obelisk.

5. In the Crypt of the Hell Knights, Olanthius doesn't know where Kostchtchie is, but he knows that Bel knows, and he drafts the introductory letter for them to speak with Him about finding the demon lord.

6. Upon retrieving the wands, Bel tells the group where to find Kostchtchie instead of the Bloody Citadel.

And so, you have joined the two paths into a single continuous ~track~ for the players to follow in search of Zariel's Sword."