Well they resized it during the upgrade anyway, just didn't change it to match the MCG. It's now wider than it was, possibly also shorter I think. And there aren't any old stands left. Trees will be gone is 20 years too, wait & see. $$$ is king.
The trees ain't going anywhere - until they die.
Which sent me to Google, and for what it's worth...
https://en.wikipedia.org/wiki/Ficus_macrophylla
Moreton Bay Figs live for over 100 years in the wild. However that article is accompanied by a picture of a MBF in The Domain, Sydney, planted in 1850.
https://southaustralia.com/travel-blog/the-story-of-adelaide-oval-past-and-present
They were planted "as far back as the 1890s"
Based on that, we might be looking at another 20-30 years minimum before the health of the trees becomes an issue enough to justify their removal.