The same thing will happen to wireless clients that happen to wired clients which have duplicate IP addresses. Connectivity for those two systems with be problematic and will include unreliable connections and intermittent loss of connectivity. You can still use “static” IP addresses with DHCP – these are called reservations. DHCP reservations make it easy to change IP parameters (gateway, DNS, WINS, TFTP, etc.) in bulk without having to visit each client computer.