Tarmac, it really depends on what you want to do after school. If your career switch is not too far off (say you want to go from B2B tech Product manager to B2C or product marketing), then you should have a good chance of trying again for full time, even without a summer internship. But for most of us, we're doing career switches such that anything in the right direction (i.e. giving you useful experience that can be leveraged for the full time job) will be good for the summer.
Therefore, my short answer is that I think you should have something in the summer that you can talk about in the fall during full time recruiting. It doesn't have to be a paid internship, as many people here at Haas look for lowly paid or unpaid internships with small startup companies that work in their field (whether it be energy, tech, media, finance, or whatever). Having the 10-12 week experience in the summer, even if it's unpaid, will help strengthen your resume that much more when you have to face recruiters again later in the year.