City would never rely on him to fill a gap vacated by KDB, Bernardo or Mahrez. If ever one of them three left, City would get into the transfer market before relying on Grealish. The definition of a luxury player, someone who has ability but not reliable. Its also not that he isnt getting in the City team, I reckon he would find a tough time cracking the first 11 at the other top 6 clubs. I for one wouldn't pick him over anyone of Odegaard, Saka or Martinelli. I doubt he would fit in at Tottenham given their 3 at the back and use of wingbacks formation, likewise Liverpool with their 4-3-3. He isnt physical enough with the engine to match to play in that formation. Would be very surprised to see him make the United and Chelsea 11 too. I think I saw a stat that he has completed 90 minutes less than 5 times since signing for City. So even when he does get a start, he is almost always the first one to get subbed.
He will either be a depth player at City, or Villa might deice to give back 50m of their fee to being him back.