For vegetarians Mostar is no good place to eat out. Sadrvan seems to be at least in some degree the best choice.
When I was there I sat outside in the nice summer garden which is why I can't say anything about how it is inside.
There were a couple of vegetarian dishes but if you are vegan you can be lucky if you have at least 1% of the whole menu to choose from (excluding beverages). I had a risotto with mushrooms (and parsley and butter) which was pretty fair, I am even tempted to say it was quite good. But I have to add that the cutlery wasn't very clean, one paper napkin they gave me had already been used before and on top of that I found two hairs in my risotto, one presumably from someone's head and one whisker.
Further I was harassed by a cat that sat next to my chair starring at me for like few minutes feinting to jump on the table every now and then. Only after very persistent ignoring the cat vanished eventually.
In my opinion it is not worth to order a dessert. I tried the most expensive one which was not good.
On balance Sadrvan was rather disappointing, besides somewhat overpriced. I have to add they gave me a Sadrvan souvenir (a postcard) eventually.
If you have the facility then cook yourself, that'd be way better, especially since I have seen some very good-looking fruits and vegetables around.
Cons: not very clean, slightly overpriced