Hi,
How does your LAN traffic reach the Internet? Is there any NAT and what is the NAT pool, is it the interface or a separate NAT pool?
ping from LAN to Internet stopped most probably because return icmp packets [echo replies] are not reaching back the LAN hosts [term 4].
Adding a term to allow "icmp-type echo-reply" will still not allow any hosts to ping the public IP interface as a host trying to ping the public IP interface would send an icmp echo-request, and normally an icmp echo-reply would be sent back as reply.
As such, you could as well implement output filters to block outgoing echo-replies or other icmp-types used for reconnaissance such as timestamp-reply, mask-reply, info-reply etc from leaving the public IP interface.
For the LAN hosts to be able to ping Internet, the return ICMP packets need to be allowed through.
Cheers,
Ashvin