I don’t recall actually redeployment of aircraft for SARS, but an advantage existed in the Pacific, in that NW had an A 320 operation in NRT since the 2nd runway opened (slightly post-9/11). The rationale was to hold the super-valuable “B Runway” slots, which were issued on a use it or lose it basis, with an aircraft more suited to post-9/11 traffic. I recall taxiing next to 34R in a 320 with 150-ish folks on board while seeing UAL 777s with few heads in the windows using the same runway for the purpose of slot maintenance. I remember 320 routes to TPE, KHH, BUS and ICN. There were probably other cities that I cannot think of. Memory is a bit fuzzy but I would say we actually upgauged a bit by the time SARS came around. The 757 replaced the 320 in Asia, opening more routes. The 320 could not make GUM or SPN due lack of ETOPs (and was not practical for other routes such as BKK and SGN). Also, many of our feeds from the Mainland and Hawaii to Asia were DC-10s as opposed to 747-200/400s.
So bottom-line, post 9/11 capacity adjustments probably served NW well through SARSs.