I thought someone had suggested combining it to a single dialog, but there was some deep technical reason it was infeasible
I looked through old issues (opened and closed): the closest I could find was the Isse#12079, where the loading of the current session would prompt N times if there were N network files missing. There was quite a lot of back-and-forth (hundreds of comments), but eventually, they were able to make it work, and get a YesToAll/NoToAll message added to the dialog when multiple files from the session were not available.
Since it was feasible in that situation, I am hoping it’s also feasible here. Thus, I created Issue #16908 to see if the “Keep non existing file” dialog (when the network goes down) and the “Reload” dialog (when the network comes back) can add the YesToAll/NoToAll buttons. I don’t know whether it’s really feasible, or if it will ever be implemented, but the request has at least been made. Those who want this feature can go to that issue and upvote and/or watch for whether or not it gets implemented.