You could use some data to let Adopt A Project deal with abandoned projects (case : the coder didn't bother updating the file).
You can check :
- last update vs frequency of updates before,
- date of the last issue the dev corrected vs date of the last issue entered
- keywords in last issues and readme
This would help dig out unmaintained and abandoned projects.
You can also send mails to some developers through the bot to check if they are still planning to maintain or not.