At some point long after the Sixth Doctor was forced to abandon Peri on Thoros Beta, he comes to Krontep twenty years into her reign as queen to apologize. The Doctor in this story isn't specified, though based on the description and time of writing it might be an older Seven close to his regeneration in the TV Movie. The story itself is rather sad and haunting (and has since been contradicted by later stories). But it is well-written and a quick read. If you're interested in a take on Peri's fate after her departure, I think this is worth the read.