Answer:
In this situation, the manager should still go on with the merger if that is the best financial choice for stockholders.
Managers main, and essential goal, is to run the company in a way that maximizes value to stockholders, so, if the merger achieves that, the manager should absolutely carry on with the merger even if some employees end up losing their jobs as a result.
However, this does not mean that the manager should not try to save as many jobs as possible.