I've been part of a company that purchased another, as well as part of a company that was purchased. In both cases, the changes were slow, with integration between technology, departments, and the org chart often taking a year or more.
Apple buys a new company every month, or every 3-4 weeks according to this article. That's about 15 companies a year, which seems like a lot to me. The cheapest part of this entire process is likely the purchase price of the company. The cost in productivity, in changing habits, correcting mistakes, and other integration tasks is likely high.
Apart from the human aspect, integrating data is another issue. While some companies can use separate systems, there will be some exports and imports of data, not to mention the potential mistakes made by employees using new systems. That's work for us data professionals, as much of the time help desks or support systems might not have the tooling or access to make changes.
Then there are the challenges of dealing with triggers or even a lack of referential integrity, which can result in tedious editing of fields by DBAs or other privileged users. No DBA? Developers might have to take time to fix things.
On top of all this, auditing is likely a concern in public companies whenever we are changing data. I used to save scripts and put them in public folders, as a cheap way of auditing. However, these days I think I'd use XEvents tied to my userID (or all domain admins) and ensure that all activity is captured.
Those of us that work with data ought to be worried and concerned about all of our data editing work. Often if there are mistakes have are widely noticed, we should ensure we have records that show we are following the proper procedures for our organization. It might not prevent repercussions, but it does give us some protection for whimsical actions by others.