How to evaluate businesses with long time employees?

What do you think about when you see a management team with 20+ years history with the company? How likely are they to stay with the company if they aren't given equity when the owner sells?

I'd love to hear stories of any acquisitions that came with long time employees. On one side it could be great if they stay. But it seems to me the risk of them leaving with un-documented knowledge is greater if they leave. Or if they become disgruntled because they weren't told of the sale and were surprised.

I'm asking after seeing a CIM for an environmental engineering firm. I don't have direct experience in the field but I do have an engineering background.