Storm in a teacup.
Went into Hyder last summer for a few hours. No US immigration.
Came back after trying to drive up to Salmon Glacier & spent 1/2hour at Canadian Imigration checkpoint. Their scanner did not like the barcode on my passport. Very odd since the passport has been stamped numerous times by Canadian imigration, including that very same Stewart one on previous trips plus we had entered Canada not 2 weeks prior & it was stamped then.
Oh well.
As for the residents of Hyder I am sure that they will go right through any barrier should a tsunami be coming their way. Besides, all of us daytrippers are back into Canada long before the border is closed for the night.