Nostalgia might prove to be an emotional guardrail for sports fans during the coronavirus crisis, so let's test our long-term memories and go way back to when the Minnesota Vikings had:

• The best receiving duo in the NFL.

• More talented cornerbacks than they could fit onto the field.

• Defensive line depth that made their locker room look like backstage at a WWE event.

• No quarterback signed past 2020.

• A slew of young, core players signed to long-term deals.

Those were good times, this era of Vikings football that existed … eight months ago.

Rapid change isn't unusual in the NFL. Thirteen months ago, Tom Brady led the Patriots to a Super Bowl victory over Todd Gurley and the Rams. Today, Brady and Gurley are NFC South rivals.

For the Vikings, though, a mass exodus of defenders and the trade of a star receiver aren't random. It's a combination of the inevitability of shedding older, more expensive players, and a result of the philosophical shift that might have led to the Vikings' playoff victory in New Orleans but could lead to major problems for the franchise in the near future.

On March 15, 2018, the Vikings signed Kirk Cousins for $84 million over three years.

On July 31, 2018, the Vikings signed receiver Stefon Diggs for $72 million over five years.

On Aug. 12, 2019, the Vikings signed receiver Adam Thielen for $64 million over four years.

Sometime between the signings of Diggs and Thielen, Vikings coach Mike Zimmer decided he wanted the Vikings to become a running team featuring Dalvin Cook.

That decision led to Diggs' disgruntlement and his being traded last week. Vikings General Manager Rick Spielman received an admirable return in draft choices; he also weakened the 2020 team's starting lineup.

That decision also means that the Vikings and Cook face one of three possibilities this offseason:

• Cook plays on the last year of his contract, a risky proposition for a running back.

• Cook holds out, or sits out, in 2020.

• The Vikings sign Cook at a price he finds agreeable, adding themselves to the list of teams taking an unreasonable risk on a position defined by sudden declines.

With Diggs gone, the defense in flux, little money left under the salary cap and the offense built around a running back, the Vikings suddenly feel more fragile than promising.

And they are now more dependent on Cook remaining healthy and performing spectacularly than they were even last year.

Cook suffered a major knee injury as a rookie. He has played in 29 of a possible 48 NFL games.

Gurley suffered a major knee injury in college. He has played in 73 of 80 NFL games.

In Gurley's best season, he amassed 2,093 yards from scrimmage and 19 touchdowns, in 2017.

In Cook's best season, he amassed 1,654 yards from scrimmage and 13 touchdowns last year.

Gurley followed his best season with another productive campaign that led to an appearance in the Super Bowl, but he began to decline in the playoffs that year, wound up sharing time, and fell to a career-worst 3.8 yards per carry last year.

This week, the Rams cut him, two years after signing him to a four-year, $60 million contract.

Cook might be a more spectacular runner than Gurley, because of his acute cutting ability.

But Gurley was more productive and more durable, was considered a possible league MVP for two seasons in a row and went two steps further in the postseason, yet there is no doubt the Rams made a mistake by extending his contract.

The departure of Everson Griffen and Linval Joseph and a dearth of experience at cornerback, added to the trade of Diggs, mean that the Vikings will be even more dependent on Cook to keep opposing offenses off the field, relieve pressure on the passing game, dominate time of possession, and to remain healthy and productive.

The Vikings need Dalvin Cook more than ever.

It's a bad place from which to negotiate.

It might be a bad place from which to run a contending team.