Just like with replies to Side Conversation in Zendesk Support, the Notifications and commands to Open Items (Tickets, Users, etcetera) will not occur if the receiving agent is not online. This means the command will expire automatically and not be shown.
Our goal with Toolbox is to deliver a solution that does not require many resources of your agent's device. Because of this, we do not save undelivered commands from Toolbox and all information is running natively on the Zendesk platform without any third-party data storage in between.