In my experience, product people who know what they are doing have a huge impact on the success of a company, product, or service. They also point engineering efforts in the right direction, which in turn also motivate engineers.
I saw good product people leaving completely destroy a team, never seen that happen with a good engineer or individual contributor, no matter how great they were.
I have seen firing a great/respected/natural leader engineer result in pretty much the whole engineering team just up and leaving.
It's different with engineering managers (or team leads, lead engineers, however you want to call it). When they leave, that's usually a bad sign.
Though also quite often when the engineering leaders leave, I think of it as a canary in the coal mine: they are closer to business, they deal more with business people, so they are the first to realize that "working with these people on these services is pointless, time to jump ship".