Cybersecurity is already a billion dollar industry and it will only get bigger. The risk will always be there with anything related to computing but companies will have no choice but to invest heavily to prevent hacking and liability. The most simple answer I can give is that AV's will always have an administrator override feature that allows the owner/company personnel to manually shut off and "lock" the car if it were to be hacked. Similar to how your iPhone can be locked when someone tries to hack into it.