How long will the Ponzi Scheme last?

Many have commented that the public housing scheme is another Ponzi Scheme or something similar in nature. In all sense, it will die a naturally death by the time the lease expires in 99 years, all 900,000 of them. On that day, all will be worthless. There seems to be a way out though, to extend the game, by SERS, whereby the HDB will buy back the flats before the lease expires, offer the lessee a new flat of the same market value or slightly more. The lessee will be happy to get a new flat for a smaller fee and a new lease. This option of buying back and offering a new flat can go on and on provided certain conditions are present. Without these conditions, the renewal and new life will still come to an end. The first condition is that the flats to be acquired are low lying, and on the same plot of land a doubling of the units of flats can be built. A 10 storey block can easily go to 20, and 20 to 40. After that it must go to 80 or 100 storeys so that the cost of building the new flats can be paid by new lessees. As the cost of building is going to be much higher, and there is inflation to add on to the cost, it is also assumed that the income of the new lessees will go up proportionally to pay for the much more expensive flats. Or else, the aspiration will be for smaller and smaller units or smaller in size like what is happening now. The third condition is that there must be more and more buyers to buy the new flats. As the formula is based on the doubling of the units, if all the flats are to be rebuilt, it will need a doubling of the population, from 5m to 10m. So the floodgate for foreigners cannot be closed. The fourth condition is that the island will not sink with all the Towers of Babel loading on it. And hopefully, the supporting infrastructure to house the kind of population density can cope with the increase. If all the conditions are met, the Ponzi Scheme can go on and on.