As far as I understand it, when the current marketplace closes any plugins that are activated against your account, either free or paid, will just download to your local install. In which case it wouldn’t matter if it’s abandoned or not.
What might affect you though is if a few months later you set up a new computer, install Corona, and then come back to look for that plugin for a new download. If the developer has indeed abandoned it then they’re not going to have migrated to any other marketplace. I don’t know if Rob / Vlad are planning to keep the current plugin tree anywhere long term…