The Seattle-Arizona game in Week 17 could send the winner to the playoffs as the fifth or sixth seed in the NFC.
NFC Standings Through Week 14
I've put together a couple scenarios using ESPN's Playoff Machine.
This one would send Seattle to the playoffs at 9-7. This one would send Arizona to the playoffs, also at 9-7. Both scenarios had the New York Giants and Detroit Lions finishing 9-7, with Seattle or Arizona prevailing on a tiebreaker (best conference record).
Tweaking those scenarios to knock Atlanta from the playoffs sent Detroit in the Falcons' place, with Seattle or Arizona becoming the fifth seed. I tried to find a way for both the Seahawks and Cardinals to qualify for the playoffs, drawing up one that improbably left Dallas 7-7-2 and the Giants 6-8-2, but did not immediately find any (not sure if it's possible).
The Seahawks finish with St. Louis (home), Chicago (road), San Francisco (home) and Arizona (road). The Cardinals finish with Cleveland (home), Cincinnati (road) and Seattle (home).
The chart shows how NFC seeding reads with the Giants-Cowboys game in progress. If the Giants win, they would hold the tiebreaker over the Cowboys for the fourth seed on head-to-head results. If the Cowboys win, they would lead the Giants in the standings, making them the fourth seed.
The 49ers hold a tiebreaker over New Orleans for the second seed based on a better conference record. The Falcons hold a tiebreaker over the Lions for the fifth seed based on head-to-head results.