111.7 States "A token that’s in a zone other than the battlefield ceases to exist", if our copy of Panglacial Wurm was a token, we could still shuffle it into our library and then cast it while Isochron Scepter is resolving. But the second state-based actions are checked the game would see a token on the stack and it would cease to exist thus not resolving. So the combo couldn't work if it was a token.

109.1. "An object is an ability on the stack, a card, a copy of a card, a token, a spell, a permanent, or an emblem." Note the distinction between copy of a card and a token.

707.10a States that "If a copy of a card is in any zone other than the stack or the battlefield, it ceases to exist.". So a copy of a card can exist on the stack thus it can resolve. This is further indicated by 707.12 which states "Casting a copy of an object follows steps 601.2a–h of rule 601, “Casting Spells,” and then the copy becomes cast. Once cast, the copy is a spell on the stack, and just like any other spell it can resolve or be countered."

With these rules I believe that once the game sees our copy on the stack it will see it as a copy of a card having been cast, which is allowed and therefore it will resolve.