Technically this would be possible. But overall i don't like the idea of storing notifications for such a long time. This whole notification concept is mostly about being quick. IMO it just does not make sense to deliver a notification days after it has happend.

Let's assume the common usecase of notifiying at 0 confirmations (for informing customer) and e.g. 6 confirmations for actually starting delivery of goods.
If the shop system would be offline for several hours there would be two notifications in the queue, each retrying every few minutes. If the shop comes online again it could happen that the notification for 6 confirmations comes in before the confirmation for 0 confirmations. This might not be handled well in the shop system.
On my side each notification is a completely independent event, so i can not define dependencies between different notifications (and i want to keep it that way for maximum modularity/scalability).

If you know your shop was offline for some time you can already now look up all failed notifications in the notification history (reminds me of the missing search/filter options there...).

An additional option would be adding a button to the dashboard to manually retry failed notifications. Maybe this would be a possible compromise?