I don't think they'd both survive. Mostly, this is because Seattle will be looking for an AHL location, it won't be Portland, it really won't be California, and with Vancouver biding their time before ending their Utica affiliation, I think an Abbotsford/Everett AHL pair is about right. That's one way of saying that, while both clubs draw about average, it's not enough to head off what's going to happen when the NHL "graces Seattle with their presence." The baseball model (Tacoma is AAA, Everett is Short-A, both affiliated with the Mariners) is a key precedent.
Unless the WHL scrambles to find owners who want to build their own American arenas, I think, no more than 20 years down the road, it's the end of the US Division in the league. I do tend to think the following is possible, however:
Maybe Nanaimo happens, but probably not.
The league liberalizes territory rules just a bit... so that Surrey and Langley can co-exist. Perhaps even a third club in the area?
Too much ego to allow a folding. Spokane could well be a long-term holdout, too... the oddball thing being the rivalry with Kootenay.