He was planning to leave on the eve of the local elections.

At what point do Reform become the Tory party, and surely that puts off Reform voters as they all rejected the Tories at the last election?
Plus, Nige likes to be in sole charge, cannot see him juggling a lot of big tory ego's who will all want to oust him at some point (Jenrick especially). I can't help thinking all the defections are going to backfire spectacularly.
If Badenoch had any sense (haha, yes, I know), or if the three remaining sensible Tories (haha, yes, I know that too) could seize the moment of Jenrick's departure, they could drag the Tory Party back to a pragmatic pro-business, pro-EU position, which served them electorally pretty well until the 'bastards' staged their Brexit coup with the aid of Chancer Johnson.
That is the only sensible option, but common sense and reasoning has been strangely absent from the Tory Party for some a good while. You are right though, this is the perfect moment for a complete reset (and possibly the last chance they will have for some years?). If anyone at HQ had any political acumen, they would abandon the Reform tribute act, start trying to claw back those that defected to the Lib Dems and try and bring back some of the old big hitters that Johnson/Cummings purged.