All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The ruling regarding what remains of that money depends on the intentions of the donors. Thus, if they intended by their donations to dedicate that money to the treatment of the sick person only, then the remaining money should be given back to them.
But if they intended to give that money to that sick person to spend it however he wills, then he has owned that money exactly as his other money. Accordingly, what remains of it should be given to his heirs and divided into the shares Allaah The Almighty has enjoined regarding the estate. For more benefit, please refer to Fatwa 196831.
Allaah Knows best.