Here is a version with a timeout so that after an amount of time the loop ends with an error:
# After 60 seconds the loop will exit
timeout=60
while [ ! -f /tmp/list.txt ];
do
# When the timeout is equal to zero, show an error and leave the loop.
if [ "$timeout" == 0 ]; then
echo "ERROR: Timeout while waiting for the file /tmp/list.txt."
exit 1
fi
sleep 1
# Decrease the timeout of one
((timeout--))
done