If the PB backfilled with the clay they dug out to set the pool, in 5-10 years there will be NO chance of collapse to drain and install new liner.
You could actually remove the entire pool and replace it with the same size and the hole would already be dug out, lol.
Once clay is either compacted or sits for several years it sticks together and becomes solid and hard again.
Clay does not absorb water like regular soil does either, BUT, as it becomes saturated it will expand, and as it dries out it will contract.