There are no Washington Statutes on commercial leases,except those found in RCW 59 12,which addresses evictions (unlawful detainers). Commercial leases are not covered by Washington's residential landlord tenant act. If your landlord lost the building to the bank,you probably want to find the person at the bank, possibly through the court filings related to the foreclosure and discuss your options with them. It may well be that the new purchaser wants to retain your business as a tenant; it isn't possible to give you advice on these limited facts.
The subsequent purchaser *can* evict you when they have standing as your landlord. The real question is whether they want to, or not. Hope this helps point you in the right direction.
When a foreclosure sale occurs, it extinguishes all interests in the property (including commercial leases) that are subordinate or "junior" to the deed of trust, provided that the holder of the junior interest was given notice of the sale. A lease is junior if it was signed after the deed of trust was recorded. The tenant has 20 days after the sale to vacate or face an unlawful detainer action for eviction. Having said that, most banks or other lenders would prefer to keep rent-paying tenants in their building, especially in the current market, by either recognizing your current lease or signing a new one.
You definitely should consult an attorney about your specific situation as soon as possible.
PLEASE BE ADVISED: This answer and any information contained herein is not intended to be treated, and should not be construed, as legal advice. Rather, this answer is offered solely for general information purposes. This answer does not create an attorney-client relationship, nor does it create any kind of legal relationship, duty, or privilege. This attorney is licensed only in Washington.