How to know if water has evaporated from curry/stew?
Rather than making the whole dish then boiling off the water, you might have more success by changing the order of your steps. For example, you could:


Add all of the meat and resilient vegetables
Then reduce the sauce until you've achieved the desired consistency
Add the leafy greens right at the end 


As far as knowing when it's reached the right consistency, that can only really be achieved by stirring it and keeping an eye on it. You're also better reducing it at a simmer rather than a boil, as the higher heat can take it past the point you're looking for very quickly.