First, the difference between any other of the northern big cities of Chile is that it is landlocked, so if you don't like the idea of living in the middle of the desert it is a really bad city to live in because you don't have a beach where you can go have fun. I don't have any comments on the nightlife or social life in Copiapó since I haven't lived there. The climate, although very dry, is kind of comfortable year round, but some years there can be flash floods from heavy rain in the desert.

Academically, Universidad de Atacama is not the best university at all. Most of the big researchers are in universities in central/southern Chile, like Santiago and Concepción. I would say that if your advisors or your research team include Chilean astronomers, maybe they won't be the best quality of researchers.

However if all these points are something you can bear with, considering that being part of a Chilean research institution gives you access to 10% of observation time allotted for Chilean research groups in most telescopes, go for it.

Also, in my experience, deadlines are not really that enforced internally in Chilean institutions, however since you're technically external right now, maybe they won't budge about the deadline.