Yes that's fair enough. But that's not what Remoaners are proposing.
If after we have exited people want to campaign to rejoin and a party seeking to rejoin wins a general election then having a rejoin referendum would be reasonable. Whether the EU would even want us back after all this and on what terms is another matter.
However die in the ditch Remoaners aren't seeking to have a rejoin Referendum after we have exited. They want a "do we really exit" one before we have even exited. That's not the same thing.
If Jeremy Corbyn wins an election he will become Prime Minister. It won't be a case of "are you sure, let's vote again first before that happens".
If Labour wins they become the government.
Since Brexit won we need to Brexit.
What happens after that is up to future elections but the last election results need to be honoured before the next one happens.