How hard is it to re-enter academia as a postdoc in mathematics?
The possibility of getting a postdoc starts to drop rapidly as you become farther away from your PhD, regardless of what you are doing in the meantime. This goes double (or triple) if some of that time is spent without having publications.

What is your end goal? Certainly not to hop from postdoc to postdoc for the rest of your life. Answering this question will probably help you decide what to do. Take another postdoc if you are hoping to become a professor or academic researcher. Take a software development position if you are wanting to leave academia. Don't hold on to too much hope of being able to go back to academia in pure math after leaving for more than a year.