I was asked recently what my ideal scenario to retain me long-term, and it occurred to me, after answering otherwise, that there does exist such a situation. Our new overlords would have to spin us off and let us operate independently, as a wholly-owned subsidiary.
My own role has not been rendered completely irrelevant, as I had feared, just stagnant. The closest thing I currently have to a boss managed to finagle our keeping our own deployment process and administrative control of our servers. For now, this means the hosting provider. Later, it means mostly virtual boxes in eBay's datacenter(s). It probably won't be significantly worse than what we have now, since our provider's internal network has had numerous failures.
However, since my next step, right before the acquisition, was going to be to move to our own datacenter, there will be no moving forward. I'll be stuck with the already outgrown scaling (for lack of a better term) model and no control of the network, hardware, or provisioning. The most powerful tools with which I am adept won't be available to me.
There will also be no opportunity for mentorship or participation in hiring other sysadmins, something I have found adds significantly to my overall job satisfaction. No, joining eBay Ops (cue "Central Services" jingle from Brazil) is not an option, since I enjoy being productive.
If we were spun off, the lip service given to continuing what we were doing, just with eBay's resources behind us, could actually be made to be true. We would be free of the usual bureaucratic encumbrances, all-downside purchasing process (no buyers, just forms), crippling "collaboration" tools like Exchange and Skype, and the temptation to shoehorn what's still a nimble startup operation into a nearly immobile behemoth's infrastructure.
We could still sub-lease their campus and maybe even be eBay-galaxy-of-companies employees so as to share benefits (though even those are lackluster and an administrative time sink). However, we would control our own destiny in terms of hiring, purchasing, and operating our service. Integration with eBay's services would be via API, as it would otherwise, since the code bases have, to put it mildly, irreconcilable differences.
I very seriously doubt, however, that this could ever happen, since there's too much potential for loss of face somewhere up the chain of command. In the meantime, I'll continue to help in what ways I can and be on the lookout for another suitable startup.
 Unless it's over a million dollars. The purchasing department has a great scam going. They've managed to appear to have very low costs, because they outsourced everything one might think they do. The accounting work is off-shore, and the request, quote, purchase, and receiving tasks are all pushed onto all employees in the guise of self-service. Of course, it's still Purchasing that dreams up the Byzantine policies everyone else is expected to implement.