"You're 100% right, you should promote me so I can train more people to be able to run things. Things falling apart whenever someone goes away is a key sign of a bad leader, not a good one. I think I've demonstrated that I've managed this department into where it can function smoothly without me needing to put full time into it and I'd do well with an opportunity to move some other things in the company forward."
"Hey, unrelated question, what's your boss's contact info?"