I'm not aware of any owner chucking in £100m+ and then pulling back after first round of investment. That level of spending is not we'll see what we can do, it's we'll get there by flooding with cash.
If there is an issue with the investment, it will still fall at Walsh's door before there is any plug pulling.
The examples of owners shutting up shop, often coincide with owners finances reaching breaking point or after multiple failed attempts. Most have lost a lot of money on players, and many have scaled back ambitions.
But the exit routes for the situation still point heavily towards continued effort in different direction. Not many billionaires are going to divert from the bigger path, and the stadium while still only theoretical, still holds wait in terms of ambition of club.