If it were me, I'd definitely attend the class reunion no matter what.
Literal
I [if-なら], what [object-を] set-aside [even-ても], class-reunion [topic-は] definitely attend [would-だろう].
僕なら 'if it were me' — a hypothetical self-insertion. 何を置いても 'no matter what, setting everything aside' — an emphatic expression of priority. 同窓会 'class reunion' — 同窓 'same school' + 会 'gathering.' A strong personal statement about valuing old connections.