Hi,
since pamac (especially pamac-updater) does not check the availability of internet connection, I wrote a small bash script that checks the connection before continuing.

Installation: copy this script below into file /usr/local/bin/pamac-manager, make it executable, and create a symlink for pamac-updater:

# Assuming file /usr/local/bin/pamac-manager already exists:
sudo su
cd /usr/local/bin
chmod +x pamac-manager
ln -s pamac-manager pamac-updater

Here’s the script:

#!/bin/bash
#
# Helps commands "pamac-manager" and "pamac-updater"
# check internet connection at start.
#
# Put this script into /usr/local/bin/pamac-manager
# so it will be on PATH before the actual commands in /usr/bin.
# Also make a symlink for pamac-manager:
#   su
#   cd /usr/local/bin
#   chmod +x pamac-manager
#   ln -s pamac-manager pamac-updater
#

_pamac_manager_main()
{
    # check internet connection, 8.8.8.8 is Google's address
    command ping -c1 8.8.8.8 >/dev/null 2>&1

    if [ $? -eq 0 ] ; then
        # Temporarily change PATH in order to use the original command.
        local cmd="$(basename "$0")"
        PATH="/usr/bin:$PATH"
        $cmd "[email protected]" &
    else
        # No connection! Inform user about it.
        local errfile=/tmp/no-internet-connection.txt
        echo "Error: no internet connection!" > $errfile
        exo-open $errfile 2>/dev/null &
    fi
}

_pamac_manager_main "[email protected]"

unset -f _pamac_manager_main

It works because, by default, PATH environment variable has /usr/local/bin before /usr/bin.
The script uses official pamac commands only after checking the internet connection exists. If however the connection does not exist, it gives a textual warning about it inside a text editor window.

Please try this and report any issues, and give potential suggestions in this thread.
If people find it useful, I could put it onto Github as a downloadable package.