Jockey pulley (upper jockey wheel) suddenly not engaging with the chain when in the three largest (easiest) cogs on the big ring only The gears work fine across the whole cassette on the inner ring but all of a sudden the chain has stopped engaging with the upper jockey wheel when in the big ring and three largest (easiest) sprockets of the rear derailleur.

The jockey pulley looks out of position when this happens (almost horizontal to the lower tension pulley jockey wheel - the chain then simply isn't reaching the upper jockey wheel) and the chain makes an unholy racket with the drive train eventually seizing up entirely until I shift into smaller (harder) sprockets.

This seemed to occur straight after I removed then replaced the rear wheel, catching it a little on the brake pads as I did, which resulted in a bit of a clunky removal.

Is this likely to be the result of a bent, misaligned rear derailleur?
It would help if you could post a photograph, but what I'm picturing from your description is that when you shift onto any of the three largest cogs in the back while you're on the large chainring the derailleur cage is pulled almost horizontal and the jockey wheel disengaged from the chain.

To me, this sounds like your chain is too short. Since chains don't magically shrink what I think happened was that when you put the wheel back on the bike you pulled it further back in the dropouts than its original position and now the chain has farther to go. So, I think all you would need to do is to move the wheel forward in the dropouts.

All of this assumes that you have horizontal dropouts, if you have vertical dropouts I'm completely wrong…