What would Durkon have been looking for, if he had Plane Shifted to Celestia to talk to Roy?

"Roy says we should keep tryin' to get 'is body back and resurrect 'im!"
"That was an extremely productive use of a day and a seventh level spell slot."
"Fifth, I'm a cleric."
"Whatever! I have real magic to prepare to actually reconnect with Miss Starshine!"

If Durkon had considered that Roy might know why Vaarsuvius' magic wasn't working on Azure City, presumably he also considered the very real possibility that Roy had been resurrected already and wasn't going to be in Celestia for him to find. And even beyond all of that, he wasn't going to come up with an act on a plan on his own; like Elan, he was looking to Hinjo for leadership, and Hinjo's priorities didn't include "find out what Roy Greenhilt has to say."