(*) Assuming a standard 3 degree ILS and a 3-nm, 1500' ATZ. If you want to fly the ILS to the furthest extent possible, you need to go-around at about 4nm/1200' at the latest, in order to be at or above 1500' at 3nm.
Only getting down to a 1200 ft MDA would probably work fine as I would need at least that minimum to navigate terrain between the ILS field and my intended destination strip. So if not visual at 1200 and as the approach is over the sea, just level off , hang a 180 climbing back on top and find somewhere else to land.