、。
Once it's out of sight, it ends up forgotten for good.
Literal
Eye [at-に] come-to-no-longer-touch [when-と], ends-up-wholly-forgotten.
The と here is the conditional/temporal 'whenever/once' marker — not quotative. 目にふれる is a lexicalized collocation meaning 'to meet the eye / come into view,' not literal eye-touching, and the negative 目にふれなくなる is how Japanese naturally says 'drop out of sight.' The final 忘れ去られてしまう stacks three things: 忘れ去る ('forget completely,' with 去る adding an 'away/off' flavour), its passive, and ~てしまう for irreversible completion — not just forgotten, but gone. Both the thing vanishing and the one forgetting are omitted, so the sentence reads as a general truth.