You said he had regular contact with Labour’s top brass and was adamant about it. I inferred that he had some kind of inside info as opposed to just giving his opinion.
No, not possible at all imo - Starmer has always been set on being PM, and the Labour right will be happy to keep him in place as long as he continues the marginalisation of the left, which he set about from the beginning. Barring some massive scandal he’ll lead Labour into the next GE, and even if he loses I’m certain that if he cuts the Tory majority to 20-30 or less he’ll get to stay on and have another crack, citing Kinnock as precedent.
I’m equally sceptical about the Forde report. The only way I see an unedited, no punches pulled version being published with Labour’s consent is if the main thrust of it is criticising the left for the initial leak. Absent that It will stay buried indefinitely. Different story if a legal challenge forces its release.