Rejoining is inevitable.
Once you accept that it's a matter of how.
Starmer is preparing the ground, he's going to allow EU citizens resident here to vote and he's going to lower the voting age, and on the quiet he'll encourage a fringe Labour rejoin group to steer the narrative, while retaining plausible deniability that it's nowt to do with him.
Simultaneously he'll be exploring closer ties to the EU, which will throw up a number of possible scenarios, an entirely predictable by-product of which will be the bleedin obvious, the simple fact that none of these halfway house options is better than rejoining, so rejoining will surreptitiously re-enter political discourse.
Old folk die off, youngsters join the electorate, Brexit is shown to be the disaster it is to all but the terminally mad. Starmer will let it all simmer, there'll be no top down, he wants pressure to build from below, then bish, bash, bosh! We rejoin, ten years from now at the earliest.