Running around with only 4 bolt on a 5 bolt rim won't have a drastic change. It shouldn't be a problem.
Though I'd suggest when you have time, fix it.
Replacing it is rather simple, but time consuming. You will need to have room behind the flange to be able to press it out and press in the next one. A stud is a screw which is pressed fit into its location. There are longitudinal splines which hold the stud in it's location. So if you can press/push the bad one out with the axle in, then be able to press/pull the new one through, you won't have to remove the shaft.
Pressing the old out is the most of the work. Pulling one back through is the easiest. Once you get the old one out, you could press the new one in, or use a spacer and the wheelnut to pull it through.
Clear as mud?