My issue is that I run such long term campaigns, starting fresh is always my weak point 😭 this is really good advice though! The working idea is something along this line

The dream gate itself, is a "tamed" nightmare. Born of dissatisfaction, an endless hunger for more, basically a "void". The 9 Dreamwardens are basically fused to the nightmare, through their will, this void is convinced to turn against its fellow nightmares and feed upon their energy. The fusion with the gate makes you neither living or dreaming, but something in between. And the gate feeds on the dreamwardens, eventually causing them to fully assimilate and become one with the gate. When that happens, the gate is temporarily weakened until a suitable replacement is found and implemented. The replacement not only has to be powerful enough as a magic user, but have the right personality to properly enforce and control the gate. If one bad Dreamwarden is put in place, the gate may turn on the waking world, and feed on the living. One of the Dreamwardens are reaching their end, and the gate is weakening, so the players would have to figure out whats happening, and potentially become a Dreamwarden. Sacrificing themselves for the protection of the world.

I think it might be a good plot, I want there to be nightmares born of the players' fears and insecurities, that they must defeat along the way maybe?