I don’t think the other angels would think about the loss of their leader with a smile. Now we don’t know anything about Gabriels personality. But let’s face it, Gabriel was probably a more humble leader than Michael is. Even the demons are aware of his ‘dictatorship’ You’re right, it’s nothing they should smile at and I don’t think they are. Rather Zachariel enjoying seeing how the little shit leader of theirs is struggling and losing his power.
LETS TALK ABOUT WHAT HAPPENS WHEN HE DOES LOSE HIS POWER.
Metatron complained about how Michael wouldn’t go to sleep. Sandalphon mentioned how Michael didn’t want to leave his authority to Metatron. During this contract they were supposed to come to an agreement between both parts. Perhaps Michael was fishing up a good human who could take over his power once he fell asleep and be his ‘dog’ in heaven. So why Michael wants to keep his powers other than getting Lucifers ass, not handing over his shit to Metatron, perhaps because it was in the contract.