A new boss is a new opportunity, a chance to make a fresh start. A new boss can cause anxiety, at least until you figure out his or her agenda. A new boss leads to lower trust, after all, you worked hard to make the previous one successful and he or she left you when it was time to collect your rewards.
Remind yourself of the impermanence of all things. No boss is going to last for ever. Sometimes a new boss is a relief, at other times, a new boss is an inconvenience. It all comes down to how much your vision and projects are impacted.
The anxiety of transition will be impermanent as well. Channel your energies in the script for “house training” your new boss, so you have a change to influence your working relationship.