While there is always a possibility that you could lose your job, and no one out there in today's workforce should ever feel confident enough in the permanence of their position that they aren't always thinking of doing better, moving on, you're borrowing trouble if you assume you need to jump right off this ship immediately. Especially as my colleagues have informed you, since you might end up owing the new company owners $3K for your relocation back there less than 18 months ago.
You do not know for sure that they are going to close your department yet, do you? There've been tons of rumors, sure. But in my experience with buy outs, closures, and so forth it seems like the people who have the worst outcomes are the ones who try to avoid the whole worry, jump off the ship quickly and run to the next thing they can get hold of, just to avoid the possibility of a lay off, closure, whatever. They tend to make "frying pan into fire" jumps.
Begin a nice, slow, controlled surveillance of the job market. Have some good ideas worked up of places where you might like to move toward. Do everything you can while still with your company to improve your hireability. Start applying for the really really good ones. You certainly do not want to be applying for jobs that pay less, just on the off chance you might have to leave this one. Those are for if you know for sure you're gone, and you're already severed from your company not by your own choice. Of course if you come up with something new that is just jim-dandy, better than what you've got now, you might decide to go on and take it, that it was worth the risk of having to pay back the relocation fees.
It is most likely, it appears to me, that the new company, if they closed down your department and laid you off before the 18 months was up, would be the drivers of the situation in which you left, and therefore you would be much better off to wait and let them terminate you, if they're going to, so you would definitely not owe them any money. You would be able to draw unemployment insurance if there was any down time between working there and the next job, IF it happens.
