There is at least one utility that can do this -
Follow-Up Reminders - Sperry Software - at $30, it's probably cheaper than trying to do it with macros (and it will be more efficient).
I don't have any macros that do this... i would probably set a flag on the sent message then check incoming messages that begin with RE: for a match in the sent folder and turn the reminder off if a match is found.
Or... just set the reminder on the sent message then use a reminder macro to send a message when the reminder fires... but you'd either need to mark the sent item complete yourself or use a macro to match the incoming message to the sent. If you use conversation view, marking the sent item complete yourself should be easy enough.