How to write AppleScript for clicking an OK button on a custom dialog?
You might simulate pressing command-Q and return instead:

delay 0.5 -- time to release modifier keys if for example the script is run with command-R
tell application "System Events"
    set frontmost of process "Live" to true
    keystroke "q" using command down
    keystroke return
end tell


Or use ignoring application responses so the quit command doesn't block the script:

delay 0.5
ignoring application responses
    quit application "Live"
end ignoring
delay 1
tell application "System Events" to keystroke return