Pros and cons of double majoring vs a Master's
In general (and from the perspective of academia) I would say many undergraduate students overrate the value of double majoring and misunderstand its importance. Having two majors does not make you an expert in two fields. Moreover, depending on the fields in question, it doesn't aid your ability to go onto graduate school.

All things being equal a masters degree is 


more useful for employment (I've never seen a job that explicitly requires a dual major but some jobs list a masters degree as a qualification).
a better indication of academic ability in a field
a more impressive credential than a dual major.


But there are several things that could make things unequal.

First, there are cases where showing a background in two fields is valuable, because a job bridges two skill sets. As aparente001 suggests in a comment, majoring in administration and art might better show an aptitude for managing a gallery than just one or the other. (Another example: a patent attorney often has a degree in science).

Second, there are cases where a graduate field requires knowledge (or some competency) in multiple underlying fields such as materials science (chemistry and engineering).

Third, if for personal reasons you desperately want to study both because you believe you will never be able to study the other after you go to graduate school, then it might be worth it to someone to spend 1 or 2 years to do that.

While there may be other special circumstances that make sense of it, I would say it's unlikely that the value towards academia of getting a second major is worth two years that could have been spent on an MA.

(For the record, I did two majors and don't regret it -- but I finished both in the usual 4 years).