Warlock in Mystara: Eternal Proxy
by Marc SaindonBasically, when you make a Pact with a Patron, you're bound eternally to your Patron and cannot ever become an Immortal or succeed on the Paths of Immortality. You can upgrade as a proxy, so a Pact of the Fiend could upgrade you as a full-fledge (NPC) Demon, but straight up Immortality is impossible as Warlock status disqualifies you on any path, even the Path of Entropy: your actions only serve your Patron, who probably PPs for this.
A Warlock that successfully break his Pact could, at the cost of his Warlock abilities, re-qualify for the Paths. Or perhaps, if he successfully destroys his Patron and takes his place as his "heir"...
(It might explain one version of the Tiamat-Venger dynamic, with Venger realizing he got cut off from greater power by pledging himself to lesser, but more immediate power)
(Image from: https://www.deviantart.com/ruizmachuca/art/Venger-989620655)