If I were holding a large amount of Bitcoins worth millions of dollars, I would start cashing out right now before it's too late.
Think about it deeply, either split happens and value halves in less than half of the current value or everything will go smooth.
But if split happens then imagine that your coins will be priced 50% less for almost 2-3 years before the market gains the trust and starts growing again.
Are you willing to put millions of dollars on hold for 2-3 years?

A private key is forever a private key. Don't worry about "changes in the code" because you will be able to cash out your Bitcoins the same way you can right now just by restoring your wallet with your seed or by importing your priv key.