10 Stargate Storylines That Were Never Resolved
7. Did Daniel Ever Check On His Grandad?
In the episode Crystal Skull, Daniel Jackson spots an artifact through MALP telemetry that is reminscent of something his granddfather, Nicholas Ballard, discovered years previously. In that encounter, Ballard claimed to have been transported to an alien world after coming into contact with the titular skull, though he was mocked by the academic community when he tried to publish this.
When Daniel vanishes after coming into contact with the new skull, Ballard is brought in to the SGC to help in the search. Daniel has been phased out of our reality, and Ballard can see him and hear him - though only he can. They all travel back through the gate to the planet where they found the skull, Ballard convinces the aliens present that they are not a threat, and elects to remain behind.
As far as we know, he is still on the planet with those aliens - aliens who exist outside of our space-time and are enemies of the Goa'uld. These aliens (and of course Ballard himself) are definitely something worth revisiting to discover just what exactly is going on there!