Labour can't function when significant chunks of it's old supporter base switched to the conservatives over Brexit.
Things need to be redrawn, they need to do an old school merger and reinvent themselves. This ties into what
@BigOscar is saying about Labour losing to the most reviled Conservative party candidate in decades, and after 10 years of conservative rule that's been awful for most people.
It's just not a party capable of winning an election in 2020. We need a left of centre party without 100 years of shit baggage and preconceptions.