This plugin will checks and if any scheduled posts have been missed, it publishes them.

Checks to see if any scheduled posts have been missed. If so, it publishes them. NOTE: This plugin is meant as a stop-gap until you and your web host determine why the built-in WordPress Cron Scheduler is not working. This plugin is not designed for continuous use on large sites that have over 10k of scheduled posts or heavy traffic.

Auto publish future/scheduled posts missed by WordPress cron