According to the documentation,

# If enabled (set to a value greater than 0), Shopkeepers will check for and
# remove the shops of inactive players once every plugin start. This setting
# determines how many days ago a player's last login has to be in order for the
# player to be considered inactive.
player-shopkeeper-inactive-days: 0

I'd like to request a feature + config option that sets shops "For Hire" instead of simply removing them. My suggested changes:

• Add player-shopkeeper-inactive-remove config option that can be set to true to remove shops, and false to set them for hire instead
• Add player-shopkeeper-inactive-hire-cost config option that accepts a number which correlates to the amount of currency-item the shop will cost to hire