If it becomes impossible to get through the NWP, they would have to transit the Panama Canal. The Otaru to Guam trip should be unaffected. The Nome to Otaru trip is a whole other problem.
The Nat Geo ship ended its trip in Resolute and I imagine the passengers who were to board in Iqaluit will instead board in Resolute and then sail the eastern half of the Canadian Arctic back to Greenland.
I think the Silver Explorer is the only ship that needs to go all the way through. I really hope the ice situation changes and soon!