Is there a way to have an AWS Lex chatbot send a follow-up response to a user if the user has not replied after a certain amount of time?
Lex responds to direct inputs. Lex, by itself, will not prompt the user to engage if the user does not respond within a specified timeframe.
That is custom logic that you would need to implement outside of Lex.
AWS Lex Chatbot - Send user a follow up message if no response detected