How to handle theme activation errors?

I am trying to implement the hook for activating a theme, that will install composer dependencies upon activation. In trying to figure out how to handle whether or not the vendor directory exists, I was wondering how to display the dependency errors if they occur, and what I can show instead of just a broken site. Also is there a way to maybe rollback to last theme, and send a notification that the theme is not able to be installed on the users system?