Successful survival strategies for academic departments threatened with closure
Once you are threatened with closure, it is probably too late to fix your problems.
Increase enrollment of new students with marketing.
Increase retention of students with better teaching and extracurricular experiences.
Seek donations.
Find a new source of revenue.
Unionize.  A union contract can force cross-subsidies from money-making departments to money-losing departments instead of closure.  However, this will not work if there are no money-making departments.

These decisions are all about money, and there's no easy way to get money.
A more detailed answer: https://ep3guide.org/toolkit