Assuming your boiler has an autofill valve (and not all do), if you shut off your water, you could have a problem. Note, normally the boiler should NOT lose water. The valve is there just in case. All modern boilers have controls that should shut them down if there is insufficient water in them.
Yes, if the boiler has a small leak, the autofill might be able to keep up and let it work while you are away, but you then still could have water damage...that water is going somewhere. If it fails to do that, either because you turned the water supply off or the hole was too big, then the boiler should shut down. Now, how well those protection circuits are working is the issue.
If the boiler shut down for lack of water, and it was cold enough, you could be in for much bigger problems.
You might want to install a new valve that would allow you to shut the remainder of the house's fixtures off while leaving water to the boiler.
A good alternative is to have someone check the house periodically while you are away.