Just by way of comparison, this is how many minutes our central defenders managed in the league last year, playing in those positions:
Garcia 788
Otamendi 1,710
Stones 1,118
Laporte 1,104
Fernandinho 2,200
If we have four central defenders and used those minutes equally, then players would expect around 1,730 minutes each. I know that is unlikely as we'll probably use Koulibaly and Laporte more together in the bigger league matches and CL; Ake and Garcia would probably start in more cup competitions but also feature in league games, too.
The odd one will be Fernandinho. He was the most reliable of the central defenders last year, but I presume he'll be happy to ease himself out into retirement.
By way of comparison, Foden managed 327 league minutes in season 18/19 and 892 league minutes last season, so Garcia is already ahead in that sense. I appreciate that the seasons and circumstances are different.
If Garcia's up for the challenge and wants to stay, then I reckon he may get the game time here over the next 3-4 years. If he simply wants to return home and try his luck there, then Barcelona should pony up.