This person didn’t get into cheaper schools this cycle. What makes you think next cycle will be any different and they will get in? There is NO guarantee they get into dental school next year. It is a competitive process, one that only gets MORE competitive every year. You are telling them to throw away a GUARANTEED acceptance for a chance at getting in somewhere cheaper next cycle.
Plus, reapplying next cycle will only delay them getting into dental school, becoming a dentist, and making a dentist salary. They are losing out on at least an entire years worth of income as a dentist. Major opportunity cost.
And schools can see if you’ve gotten an acceptance in the past, and if you’ve rejected it. Rejecting multiple acceptances will be a massive red flag on his re-application that will not help him get in anywhere cheaper.