Guardiola + Messi reunion. City already had De Bruyne, Sterling, and Agüero. With Messi, they probably win 2-3 Champions Leagues instead of just 1. The 2021 final against Chelsea? Messi doesn't miss those chances. The Premier League would have seen peak Messi for 3 seasons. English football's loss is PSG's... also loss, honestly.
Liverpool win the league. Gerrard gets his Premier League medal. Suárez stays one more year. Sterling develops with Suárez instead of leaving for City. The entire trajectory of English football changes. Brendan Rodgers becomes a legend instead of a meme. One slip, one season, one career defined.
Geoff Hurst's second goal (the crossbar one) almost certainly gets ruled out. The ball didn't cross the line — modern technology proved it. England might lose the 1966 World Cup final. "They think it's all over" never gets said. English football loses its foundational myth.
MSN (Messi-Suárez-Neymar) for 5+ more years. Barcelona never need to panic-buy Dembélé and Coutinho for £250M+. They don't go bankrupt. PSG never become serious Champions League contenders. Neymar wins 2-3 Ballon d'Ors. The best front three ever assembled stays together.