What happens to the HDB flat when 1 of the administrators pass away?

Hi!

Asking on behalf of my dad, what will happen to the HDB flat when 1 of 3 administrators pass away?

Will his share be transferred to the other 2 administrators or will it be transferred to my mum (mum has no ownership of the flat)?

Selling the house is out of the questions, as my parents prefer to stay in that area and has many friends there and my dad has mild dementia now.

Thanks in advance!