I am posting an excerpt from Mahabharata that supports organ donation:
The Deities said,-…The Asuras are being aggrandised, while we are
being weakened. It behoveth thee, therefore, to ordain what is for our
good. –After the deities ceased, the Grandsire replied, - The great
Rishi Dadhichi of Bhrigu’s race is now engaged in performing severe
austerities. Go, ye deities, unto him and solicit a boon from him. Do
ye so arrange that he may cast off his body. With his bones let a new
weapon be created called the Thunderbolt. Thus instructed by the
Grandsire, the deities proceeded to that place where the holy Rishi
Dadhichi was engaged in his austerities. The deities with Indra at
their head addressed the sage, saying,- O holy one, your austerities,
we hope, are being well performed and uninterrupted. – Unto them the
sage Dadhichi said, - Welcome to all of you. Tell me what I should do
for you. I shall certainly do what you will say. They then told him, -
It behoveth thee to cast off thy body for benefiting all the worlds.
Thus solicited, the sage Dadhichi who was a great Yogin and who
regarded happiness and misery in the same light, without being all
cheerless, concentrated his Soul by his Yoga power and cast off his
body. When his Soul left its temporary tenement of clay, Dhatri taking
his bones, created an irresistible weapon called the Thunder-Bolt.
With the Thunder-Bolt thus made with the bones of a Brahmana, which
was impenetrable by other weapons and irresistible and pervaded by the
energy of Vishnu, Indra struck Vishwarupa the son of Tashtri….
[Mahabharata Santi Parva Section CCCXLIII]
Organ donation is a splendid thing to do. It is the Atman that is important and not the physical body which is only a 'temporary tenement of clay'.