No, there is no implicit return.
If the return is missing the script will drop through and execute the next section.
Also, if there is no exit in the main code, then the script will drop into the subroutines and exit them.
There are some uses for this technique, but they are exceptional and because they make the script so hard to understand and maintain they should be avoided.
Here is a very simple example of your current scenario:
Code:
"In main" ?
GoSub "FOO"
GoSub "BAR"
; Subroutines
:Foo
"Now in FOO" ?
:Bar
"Now in BAR" ?
RETURN
The coder is expecting to see "In Main", "Now in FOO" and "Now in BAR" but what we actually get is:
Code:
In main
Now in FOO
Now in BAR
Now in BAR
Now in FOO
Now in BAR
