As of what happens if someone send BTC from a BTC wallet to BCC wallet address, the transactions go through.
But you can only see that transaction in the Bitcoin Blockchain rather than Bitcoin cash blockchain.
I will simplify with an example.
Say there is an address named "abc" in BTC and another address named "def" in BCC.
abc has 1 BTC (Bitcoin Network)
def has 0 BCC (Bitcoin Cash Network)
If a person by mistake (or for fun) sends 1 BTC from abc to def. Then the balance changes as follows:
abc has 0 BTC (Bitcoin Network)
def has 1 BTC (Bitcoin Network) [Assuming there was no transaction fees]
def has 0 BCC (Bitcoin Cash Network)
So, if the owner of def in BCC has the private key of that address, he can access the BTC in def as well.
But if he unfortunately does not hold the private key of that BCC address (like it can be of an exchange where you don't have access to the private key), then the BTC cannot be accessed by the owner of the BCC address.
Hope this answers your query well.