Q. May one break a minyan to go eat Shalosh Seudos before it gets too late?
A. It is likely as many shuls and people do, that he ate a Kiddush during the day, so in a sense he ate Bedieved or after the fact already Shalosh Seudos. Otherwise, he may just grab in shul a large enough piece of Mezonos and promptly comply without leaving the shul without a minyan.
Horav Shlomo Miller's Shlit'a opinion is similar.
Rabbi A. Bartfeld as revised by Horav Dovid Pam, Horav Aharon Miller and Horav Chanoch Ehrentreu Shlit'a.