Well, you might think, what do programmers have to do with mergers between companies? Well, many, from the novice to the most experienced will be involved in the whirlwind caused by the purchase, merger, and even by the disappearance of the company they work for. Even if it is a small company or a Freelancer, if it becomes part of a larger conglomerate then it will be affected.
Affected by what? Well, you may have to requalify 100% in the technology that the other uses, be it IDEs, programming languages, Operating Systems, networks, cloud with its XasaS services, etc.
Perhaps it will also be affected by having to implement in the "new" branch everything defined in the "new" parent company, even without having IT specialists of any nature and specialty who had worked in the branch, either because they were fired or because they do not accepted the "new" terms and resigned.
The possible scenarios are as varied as each "merger", to call it somehow, is unique, and therefore the challenges to overcome will also be unique.