safe depth to drain vinyl pool w/vinyl stairs

[ScottsdaleSwim]

I'm getting ready to drain my inground vinyl lined pool at least halfway. My husband is freaking out that we shouldn't drain it. One place on the steps has pulled away slightly (actually our realtor did it when we were looking at the house, she had never seen a vinyl liner and wanted to see what was behind it) and continues to pull away even after we shove it back in there. But it's minor.
So here's my question. I know it's safe to drain it at least half way...but even with vinyl stairs?
He's got me totally paranoid that our pool will sink through the ground and suck us down with it!

I hate the coping btw, how hard it is to change that? Curious..

Thanks.

Oh, I'm draining because my cya is over 110 now.