Gigs are one off events. Season cards are more complex. I’d assume that City will refund anyone that has bought for the remaining matches individually. Similar to you getting your money back for the gigs cancelled.
The season hasn’t been cancelled as of yet, so all the games are technically postponed at this stage. Did you demand your money back for the Arsenal game when that was postponed? It’s the same position now with that game.
We all know that the season is likely finished, with a small chance of it being played behind closed doors in about November. However, the league hasn’t officially been cancelled, so it would be carnage for City if they refunded everybody their remaining season ticket money and by some miracle the season restarted.
With all that being said, I would really hope that if the remaining £20-500 (no idea what the highest number may be) due to be taken out was critically important to that seasoncard holder, and they made City aware of it, that they would refund them of that money.