Naufragará is the future tense of the verb naufragar, meaning "to be shipwrecked" or "to sink". It's a dramatic and evocative word that paints a vivid picture of loss and despair.
In this song, Chayanne uses it metaphorically to describe his heart being "shipwrecked" on the beach, symbolizing the profound heartbreak and the end of his dreams of love. This powerful imagery makes it a memorable and impactful word in the context of the lyrics.
The whole song is one beach, remembered twice. Chayanne starts on the summer it began, when Cuando la playa / Se inundó de luz y sol (When the beach flooded with light and sun) and Y cuando el mar con su rumor / Te habló de amor (And when the sea with its murmur spoke to you of love). Then a person shows up, Llegaste tú (You arrived), and in the very next breath he names how it ends: Flor de un verano (Flower of a summer). Two words, and the whole thing is already over.
That is the trick of the lyric. Autumn is written into the summer from the first verse, so when the weather finally does its work the wreck happens on the same sand: Naufragará mi corazón (My heart will shipwreck). What follows is a quiet inventory of things that disappear while the beach itself does not. The footprints go, Las huellas de los dos / Se borrarán (The footprints of the two will be erased), the voice fades, the sand and the sea stay exactly as they were. And then he refuses all of it anyway with Aquí en la playa te esperaré (Here on the beach I will wait for you). The sun coming back in Cuando en la playa / Nuevamente brille el sol (When on the beach the sun shines again) is doing double duty as a calendar and as a reason to keep standing there.