Arm Holdings is held fully by SoftBank and the Vision Fund, should they fail, i am not sure what would happen but my guess is Arm would get out of the tumble relatively unscathed, it's too valuable.
During the dotcom boom, he became the richest man in the world for a few days by betting big and then during the crash, he lost almost all of his net worth.
https://www.quora.com/How-did-Masayoshi-Son-lose-70-billion-...
He was able to maintain power and keep softbank afloat while losing billions during the dotcom crash. So he has powerful backers and contacts who believe in him and are willing to carry him during rough times. That's very rare. In many ways, he reminds me of bezos and musk. For some reason, they are able to get the support of big money while losing a lot of money.
It may fail but it can't be a worst investment than just giving it away as dividends.