Just would need a very easy worker in JS. The use case is to fecth the response from the origin or the response that the edge send to customer (maybe that one) with status code => 500 for origin not avail. I guess it is 503 and 504.
Just a worker that fetch that status code and then it send to another site or page, instaed of as it is now (always online) sending an offline page or using cache,
thanks for the help, i am new on thse very promising workers stuff.