One of my projects was for a large, well-known dog-food brand. The iOS lead left, making me the sole developer, and the project was blocked because the hardware wasn't working — the hardware and software teams had been pointing fingers at each other for weeks. I drove over to their office, sat down with the lead hardware engineer, and we found the bug together: an uninitialized array. It took ten minutes once we were in the same room. The company eventually built an internal team to take the project over, and the product is on the market today.
That's the kind of move senior engineers make when something is stuck — you find the human who can unstick it, even if they're in a different building or a different company.