It will reach the router, obviously. If it's a TCP SYN packet and there's a server listening on that port, you'll connect to that server. If there's no listener then you get a RST.
So, assuming the router doesn't have any server running, the connection will be reset, thus protecting all of the machines behind the router from any incoming connection, almost exactly like a firewall (sure, a firewall might just drop the packet instead of responding with a RST). So, in other words, NAT alone can act like a security perimeter, even with no firewall present.
Because no one on the Internet can reach my 192.168.0.7 machine if the NAT router doesn't translate the packet. And the NAT router won't send a packet that arrives with its public IP as dstIP to any machine behind it, unless the port its ports correspond to an open connection, or to an explicitly forwarded port.
