I agree, the best way to determine if an acquiring company treats its acquirees well is to ask others who have been acquired by them. But that's kind of a separate question from how you protect yourself when you're at the negotiating table. If you talk to a bunch of others who've sold to that company and they all say it was horrible, you should wave off the deal before you ever get to a negotiating table.
I don't think waving off the deal is the only reasonable response - it is also reasonable to change your own expectations. Don't plan for a future, simply get everything you can up front. Anything else more long term than that, you should consider fluff. It can be hard to let "your baby" go like that, but depending on the circumstances it may even be the right thing for you, a chance to start over on a different project.
