Travel for the purpose of receiving medical treatment is not insured if an accident or illness occurs while you are out of the Yukon. This applies equally to the United States, Europe or any other Canadian province.
If you need an ambulance or air medevac, even to return to Whitehorse from Skagway, the full cost will be your responsibility.
An accident or illness in Haines, Alaska could mean a medical evacuation to Whitehorse at a cost to you in excess of $1500.