1) He played 88 minutes of the CL QF. Not mentioned. He was rotated and had good output vs Watford and Bournemouth. Him and Sane were subbed out about the same time vs Swansea. it looks like he lost form after Christmas and was struggling to get back until around the Bournemouth game.
2) The Daily Fail journo said this in the article title I found: "Forgotten man Riyad Mahrez threatens to quit Man City as he complains about a lack of opportunities". I read the contents of the article and all I can find is this: "The £60million summer capture has been an unused substitute in each of City's last three games at a crucial stage of the campaign. And Sportsmail understands Mahrez was making his displeasure known around the club's City Football Academy training centre for some time prior to that." and that's it.
So, he is basing a huge claim that the player is threatening to quit on the premice that his Sportsmail (a person, a group?) understands that Mahrez shows some displeasure around the CFA centre. In fact, I refer you to the interview given by Mahrez on the official site on April 17 where he gives a totally opposite statement.
3) You're right. I forgot the Palace game.