Scott McNealy would occasionally send a note of congratulations on a promotion, typically he would say "One step up, one step closer to the door." That was of course figuratively true, and in the case of building 4 at Sun also literally true since the executive offices were right next to an employee entrance :-)
As others have noted departures at this level are always much more nuanced than simply "this was bad" or "this was good." None of the departures where I was pretty close to the departee and the situation were 'unexpected' in the sense that their course had a way point which usually pointed 'up' or 'out'.
So think about your own career, think about what you want to do, what mark you want to make on the world, what things are you passionate about. Sometimes a company changes direction, from market forces or personnel changes and the company and the individual become less aligned. Its always possible to see if you can bring the company back toward alignment, it's also possible to see the cost or probability of that happening.
In my own experience I was a VP level technical contributor at a company during the dot.com boom. I arrived as part of an acquisition which was pushed by the CTO of that company who had a vision for a richer services oriented IP connectivity solution for multi-tenant buildings. A series of missteps, some poor 'chemistry' between the executive team, and a general collapse of the DSL market, made it clear that even though I had an employment contract with these folks, the place they were going (back to their 'roots' as a wiring solution) wasn't a place I would find very interesting. I talked with the CEO, we looked at all the options, and both agreed that the 'right' answer was going to be for me to leave. That didn't particularly bother me, because the parting wasn't really a reflection on my ability or non-ability, things had changed I had a choice, I chose not to follow that change.
Contrasting that for when I left Sun (certainly not as senior level as that) where I had poured a lot of energy into the product that would become Java with visions of building really strong capability based systems and light weight task specific operating systems, only to realize that Sun 'corporate' had decided that Java was the battering ram to try and deflect the Microsoft Juggernaut of Windows/NT and a growing Enterprise presence. I was really pissed off. I talked to Scott about it, Eric Schmidt (CTO at the time), and James Gosling. To their credit everyone was very supportive of my passion but in the end the company gets to decide what they are going to do with your work product, and I could not get Sun Labs to sponsor my secure version of Java and while I felt e-commerce was going to define the killer App, realistically in 1995 I was about 7 years too early to that particular party. So, just about 3 months shy of getting my 10 year pin/clock/whatever I stormed out. Emotionally I felt pretty liberated, feeling like Sun was too clueless trying to protect their enterprise accounts to see the low hanging fruit right above them.
The only place I have felt truly bad about leaving was Google, not because I was leaving, it was clear to me that Google and I had incompatible goals, but because I felt like I had failed the folks who were fighting the good fight and I left them there to suffer. The path to success there was pretty clearly laid out for those who looked for it, but the cost for me was high, too high.