Can i acces to my word addin if i am offline ?

Question

Hello everyone, I am a junior developer and I need some help with a task.
I am working on a Word add-in in React that was generated by Yeoman. We will deploy the web app on a VM and the manifest file in a shared repository.
Now, I want my add-in to store a PDF file in base64 form in Word's cache or local storage, so that it can be used when there are network problems.
Currently, the add-in works perfectly when I launch the development server. However, if I close Word and reopen it while still offline, the add-in won't load and displays a network error message.
My questions are:
1 Can I replace this error message with a personalized behavior, or is it managed by Word and cannot be edited?
2 When I close Word and reopen it, do I lose the data stored in the cache?