On a different level, Rowling understands that all magic power, including her own artistic powers must be ended. Rowling, like Harry, abjures power, and vows to end her series.
Much as Shakespeare ultimately decided to put his artistry aside. I can just imagine Rowling, standing in the Globe, vowing as Shakespeare did:
'Our revels now are ended'
Our revels now are ended. These our actors,
As I foretold you, were all spirits and
Are melted into air, into thin air:
And, like the baseless fabric of this vision,
The cloud-capp'd towers, the gorgeous palaces,
The solemn temples, the great globe itself,
Yea, all which it inherit, shall dissolve
And, like this insubstantial pageant faded,
Leave not a rack behind. We are such stuff
As dreams are made on, and our little life
Is rounded with a sleep.
From The Tempest, Act 4 Scene 1