The exit status doesn't tell you what the user did in vim. Perhaps you could compare the timestamp on the file before and after to see if it was written to?
This works for me:
echo Edit me > editme.txt
time1=`stat -c%y editme.txt`
vim editme.txt
time2=`stat -c%y editme.txt`
if [ "$time1" != "$time2" ]; then
echo You saved it.
else
echo No change.
fi