You can use $script(filename) to determine if a script is loaded or not.
if ($script(myscript.mrc) != $null) echo myscript.mrc is loaded
else echo myscript.mrc is NOT loaded
You could also test than an alias within the script file exists.
if ($isalias(myalias).fname) echo myalias exists in $v1
else echo myalias doesn't exist
-genius_at_work