The reading is, εἰ μὴ παρήσει πρὸς τὸ οἰκεῖον τέλος; and the Latin translator renders “si non segnes simus ad finem proprium.” It seems better, with Sylburgius, to take εἰ μὴ as equivalent to εἰ δὲ μὴ, and to put a comma after μὴ, so as to render as above.