For posterity: 89 Cowboys is not a valid example of tanking.
I've still yet to see a valid example of where a team tried, gave it their all, then mid-way through the season they sabotaged their remaining games in order to get as high of a draft pick as possible, and then doing that worked. That's actual tanking, and moreso the point is that it actually worked. I'm sure teams have tanked before .... but I say it has never worked.
Basically, worked can only mean you got a franchise QB out of it. Even years ago, but certainly today, it's tough to see justifying such a strategy for really any other position.
First off, it's rather difficult to prove either way, researching exactly where teams were in the standings before making a decision to not put their best foot forward to get a playoff berth.
Second, the NFL Playoff format has changed in just the past couple of years to a 7 team format. In the past, teams fighting for the 5th & 6th seeds, could have been closer to the Division Championship and regardless making into the tournament and having success would feel less daunting, getting to play the 3rd or 4th Seeds in Rd 1.
That might be enough now for teams to say, "screw it" instead of going on the road for a 3 games with a rather unfavorable matchup in their first round. Could be additionally plausible if the team "fighting" for the 7th seed is already banged up with a back-up QB or even 3rd stringer and other significant injuries.
Lastly, for it to "work" I don't necessarily have to be landing a franchise QB. Maybe a team in such a position has their long term QB solution figured out, but the starter is out for injury. A team moving from 20th in the Draft to say 12th and lands an All Pro destructive Defensive End or a Offensive Tackle, could certainly get a team over the hump for future success.
Totally plausible. But again I am not saying the Vikings should do that.
Hypothetically though, What if Week 18 the Vikings were still alive but in addition to needing to win would also need a multiple combination of Seattle, LA Rams and Tampa Bay to also lose? Even more murky would be if in addition to Cousins other key contributors were out or extremely limited. Could a reasonable case be made to play a less experienced QB or rest starters and not go full out? Sure.