If a civilisation spreads to stars then logically it will continue to spread (no technology or resource problems) and no event - not even super novas - could stop it (as events could only travel at the speed of expansion)

At that point you don’t have a single civilisation , you have thousands of functionally independent civilisations, with numbers increasing all the time. Sure something could wipe out a civ in one star system, but it couldn’t spread to others quickly enough to affect those others.

The most successful civilisations would continue to expand independently over time to take up all the resources in a galaxy.

Unless they found a way to travel faster than light, which means events could spread fast enough to collapse the civilisations.