TLDR -- I think the answer is "I'm screwed," but I'm asking here to be sure and / or out of a faint glimmer of irrational and misguided hope:

Once a BP is deleted from the cloud library, it's irretrievably gone?

Context: I hate "linking" cloud-BPs and BK-books to my toolbar in-game for exactly this reason, instead preferring to actually "create copy" from my cloud, and then subsequently manage inventory slots with "physical" copies of the BP books. That way, any mistaken deletions only deletes the in-game local copy and not the cloud-copy.

Whereas this time, for whatever reason, I had a BP cloud-linked to the toolbar (of my creative save, which is the most idiotic component of my mistake.)

Since I am very meticulous with how I version-number and update-archive of my BP books without ever intended to delete earlier copies, I popped into my creative save just now to tweak a few missing signal-wire-connections, corrected the orientations of individually misplaced pipes / inserters / etc. You know, the usual need to tweak existing blueprints.

And like a dummkopf, I confirmed the "are you sure" prompt.

Also, rant-suggestions that I will of course mention on the forums but I'm performing a public brain dump here to better organize my points by crowdsourcing them with you folks here in the subreddit:

1. Please differentiate the "are you sure" dialogue box as between deleting local-copies of BPs versus cloud-library BPs. Ideally, ONLY allow deleting cloud-copies from within the cloud-library UI. Yes, I know this has been suggested dozens of times before, like I said, I'm am idiot.

2. Please allow for some scintilla of BP-undelete functionality.

3. Possibly rendering my entire versioning scheme obsolete, any ideas on a base-game ability to version-track personal BPs? Full context, I am aware of what Github does and have a vague sense of how it executes versioning, and I'm similarly vague in my understanding of the full ramifications of what Github actually allows a software dev to do. Even in my non-software-dev level of expertise, I think it's obvious to me that asking for "full Github functionality" within the BP cloud-library is a bit silly to suggest.

4. ANY new ability (base or mod) to zoom and scroll within a BP would be fantastic. Same for within-BP ability to add entities at all, let alone the (likely unattainable) pipe-dream of manipulating entity properties / recipes / combinator logic / etc.

Edit: It occurs to me that undelete-ability could be affected by whether or not the player has closed the game client, or even closed the Steam client. I.e., there might be options to "undelete" a cloud-BP so long as the player catches it immediately before exiting the game or shutting down their computer.