Legal perhaps, but with exception of the BA flight an engine failure on a 4 holer will result in a diversion all the same. It is only prudent.
Just SLF here, but about two years ago I was on a BA 747 (CPT-LHR) that had an engine failure (so we were told) just north of Windhoek. Flew on to London anyway, which surprised and purely from a practical point of view delighted me. Welcomed by Fire Trucks next morning.