Word on the street is that there are many out-of-work mechanics being trained in advance. Given the large number of mechanic furloughs/layoffs over the past several years by the airline industry, there are likely to be many people willing to take the work.
It will be interesting to see how this plays out, because the stakes are very very high. The sunniest alternative for travelers is that the replacements are able to pick up the slack quickly. More realistically, there will be disruptions on many of the smaller/less profitable routes. The least pleasant alternative will be if the pilots and FAs honor the picket line---that will pretty much shut NW down.
I would think that late october/early november flights won't be impacted. That will be two months into any job action. By then, either NWA will have broken the union, or vice versa.
We have DTW-ORF flights 8/19-8/27 that I booked in April. I bought
trip insurance yesterday to cover me in case things don't go well. However, read your policy very carefully, because some policies consider the reaching of impasse and the cooling off period (which happened yesterday) to be a strike announcement, so it would not cover you unless you bought it
before yesterday. I bought my policy from CSA (via insuremytrip.com). According to the phone agent, because the strike is not definitely happening, it is not yet "announced" by CSA's definition.
In addition to buying trip insurance, you can ask the airline for paper tickets. This will cost you a small amount, but will save you a step if NW has last-minute agreements in place with other carriers to take their passengers. If you really must get somewhere, and cannot afford to be late, book a refundable flight on another carrier to be sure you have a seat.