Now that we know that Horatio has canonically explore the dungeon of the endless with sara, max and gork, a question remain to answer:

will He be added to the game?

Will Horatio be the last add-on to this great game?

In this thread, it was basically confirmed Horatio the First (Prime) is the author of the journal

Jeff Spock confirms this ^

In effect, you are Horatio. Hence why you can heal your allies (Gork calls him Doc for a reason) and why he is in the comic but not a playable character in the game