Re the coming general election, they are totally unnecessary in the UK because we do not elect our party leaders. We elect a party.
It's entirely possible that a party leader could lose their seat, but that their party could still win the election.
Then, or course, there would be need for a leadership election.
The PM is not our Head of State. The business of government could still carry on with an acting PM.

So, the debates about leadership debates are a lot of fuss over nothing.