Do most people who major in music finish college?

This is tricky to answer and varies by schools greatly. Right now around 58.6% of all college majors graduate in the United States according to the National Center for Education Statistics. Only 19% of those students complete their degrees in four years and there is a higher percentage of drop outs with minority ethnic backgrounds.

Now, with all of those facts listed out, they do not necessarily apply to you. For instance, if you look at Berklee College of Music:

"Overall, 54.4% of Berklee College of Music Undergrads Finish Within Six Years

At Berklee College of Music, there were 1,100 bachelors degree candidates in the class of 2013. By 2015, six years after beginning their degree, 54.4% of these students had graduated. After an additional two years, 57.0% of this class eventually completed their degree." -College Factual (https://www.collegefactual.com/colleges/berklee-college-of-music/academic-life/graduation-and-retention/, 2018).

To put this in perspective, Harvard has a 98% graduation rate (Harvard College, https://college.harvard.edu/what-harvards-graduation-rate, 2018). The best advice is to talk to your potential schools about their graduation rates within the music program and understand that the graduation rate is completely dependent on you as a student. This is just a number that represents how well the college is teaching students their material, funding their program, and getting students out into career placement. Your individual experience will depend on how well you fit into that program, your college funding, and your expectations of college.

A better question to ask the college is how many individuals are employed in their field of study after graduation. This will give you an indicator of how likely your school's program can help you land a career in the field after graduation.