It’s not a perfect replacement, but searching OpenStreetMap via https://overpass-turbo.eu/ with a query like
[out:json][timeout:25];
(
nwr["diet:vegan"~"yes|only"]({{bbox}});
nwr["cuisine"~"vegan"]({{bbox}});
);
out geom;
can be useful and is often more up-to-date with respect to restaurants that actually still exist.
An example: https://overpass-turbo.eu/s/2shI


Though HappyCow is closed-source and proprietary, it’s like OSM in that it relies on user reports. Have you submitted new restaurants and reported closed ones?