The real test of an interim manager isn't what happens while they're there. It's what happens in the three months after they leave.

If the team reverts (the processes get dropped, the hiring pipeline goes quiet, the one-on-ones stop) then you didn't change the team. You were the team. Everything you did depended on your presence, and now your presence is gone.

What should happen is boring. The team keeps doing the things that work because they understand why those things work, not because someone told them to. The new lead (or the promoted internal) has been involved in every decision. The documentation exists. The habits are habits, not instructions. That's the job.