There's a topic identifier in the form of the topic property for the $chan() identifier.

/help $chan

Window identifiers

-

//echo -a $chan(#channel).topic

Change this to your channel name.

-

You could make a topic identifier...

Code:
alias topic if ($isid) return $chan($iif(!$1,#,$1)).topic | topic $1-


//echo -a $topic(#channel)