My parents replaced a butler sink in their house as they didn't really like it. Because they are white they ate very unforgiving if they aren't immaculate all the time. They are also very hard so it is very easy to break things on them. You might be able to find a sink to fit the space but it would probably be expensive if it is an unusual size. But if you have wooden counters it night be possible to cut a bigger hole for a new sink and draining board.
I would do as her honesty suggests, try it with a bowl inside as then you can still put our dregs/rinse veg etc and this is a lot easier than trying to replace it, unless you can find a double butler sink with exactly the same dimensions.
A butler sink for a standard sink wouldn't normally be a straightforward swap. Normally has a different unit below and the worktop cutout would be cut all the way to the front. Standard sinks, sit on top of the worktop, sitting into the cutout.
In our current house we have a sink set up that is basically one and a half sinks and we love it. So even if you have a sink full of washing up you have the little half sink to wash veg, pour away coffee remains etc. We are about to move to a new house with a lovely kitchen but it has a butler sink. It looks very nice but neither of us like them in practice. Does anyone know how easy it would be to replace the sink? And are all sink units standard size so would it just be a case of taking one out and slotting the other in (and plumbing of course!). Thanks.