Even the local pub with the "Cheers" atmosphere needs to be attracting new guests.
The fact is that regulars can become irregular through no fault of what you do.
Their financial situation changes, their personal situation changes, or they may move to a different neighbourhood.
The point s that, yes, you need to constantly be taking care of the guest and providing them with an experience that makes them coming back for more.
But don't just rely on word of mouth to bring in new guests. Create a Sales strategy that concentrates on accelerating the word of mouth process and is consistently bringing new guests to your restaurant.