There have been comments on TV-Ark’s Facebook page stating Westward Diary replaced The Muppets on the Wednesday - and that it may have even been shown earlier in the week. Not sure if that’s accurate info - in particular it seems unlikely Westward interrupted the blue screen of death earlier in the week for their local news. If they did show this on the Wednesday, they likely opted out of the trailers and pre-startup menu that advertised The Muppets.
I've heard this, but never seen any proof of it, and I find it highly unlikely - as you say, the story is they came back on Monday just to do Westward Diary, which seems a bit odd. The programme at 11.15 in a number of regions on Thursday night was, rather oddly, ATV coverage of Nottingham Forest's European Cup match from the previous evening. And Mixed Blessings on Friday was a repeat, they were clearly really short of material. I would assume the Emmerdale was as well, they would sometimes show repeats between "new" series in those days.
The reference in the Cannon and Ball billing to Morecambe and Wise is because it was not long after Eric had another heart attack and there were suggestions that might be the end of the act. Eric and Ernie's move to ITV got off to a bit of a false start, they did two shows and then Eric had a heart attack, ITV went on strike and Eddie Braben was still at the Beeb.