Here is the breakdown from The Athletic. There is more, but article is paywalled, and this is the essence:
Padres
• Have clinched a postseason berth
• Have clinched a finish ahead of Atlanta
• Clinch a finish ahead of Arizona with one more win or Arizona loss
• Clinch a finish ahead of New York with a combination of two San Diego wins or New York losses
• Clinch the NL West title ahead of Los Angeles with a combination of seven more San Diego wins or Los Angeles losses
Diamondbacks
• Clinch a finish ahead of Atlanta with a combination of four Arizona wins or Atlanta losses
• Clinch a finish ahead of New York with a combination of five Arizona wins or New York losses
• Clinch a finish ahead of San Diego with a combination of seven Arizona wins or San Diego losses
Mets
• Clinch a finish ahead of Arizona with a combination of four New York wins or Arizona losses
• Clinch a finish ahead of Atlanta with a combination of five New York wins or Atlanta losses
• Clinch a finish ahead of San Diego with a combination of eight New York wins or San Diego losses (This cannot happen before Monday)
Braves
• Clinch a finish ahead of Arizona with a combination of five Atlanta wins or Arizona losses
• Clinch a finish ahead of New York with a combination of seven Atlanta wins or New York losses (This cannot happen before Monday)
One takeaway
• The Mets cannot be eliminated before Monday’s doubleheader
What would render Monday’s doubleheader completely unnecessary?
There are a couple scenarios in which the National League playoff field is set and seeded by Sunday night. This would require:
• A Royals sweep of the Braves
• The Padres to take two of three from the Diamondbacks
• The Mets to win the series over the Brewers
In these cases, the Padres would host the Mets and the Brewers would host the Diamondbacks. The Braves would be eliminated.