DNAT: forwarding all ports to a host

One requirement for a firewall setup I am working on is the ability to forward
all (remaining) ports to a specific host on the network. Note that I am hoping
to avoid using this but it is required as an option.

The server/router runs some services. There is a chain of RETURNs for those
services. Packets with the remaining destination ports fall through to the
actual DNAT target:
# iptables -t nat -A PREROUTING -i eth0 -j DNAT --to-destination 192.168.2.10

But what affect does this have on ESTABLISHED,RELATED connections? Does this
interfere with, say, a reply from google.com:80 to network host 192.168.2.99?

Links etcetera welcome.

Thanks.