I don't what changes Pep could've made to prevent this, unless Ake can play right back. KdB for Gundogan was a defensive sub.
This failure is on the players.
It wasn't a defensive sub. De Bruyne had been playing badly the whole the game and giving away possession.
This is what I posted earlier...
De Bruyne's passing has been off this game. Also his tactical awareness has been suspect. If they had to win this game they'd probably bring him on for a Gundogen.
They'll probably go with Sterling for Foden/Mahrez and go 4 in midfield to seal the game; or Gundogen for one of the two wingers and play a possession game.
They should have switched to counter attacking game after going one up.