Would not the critical point re engine failure or rollback (other than severe damage considerations) be primarily concerned with drift down to E/O cruise altitude and being able to make the nearest suitable or adequate with the appropriate reserves.
If sufficient fuel is on board to make destination (plus required reserves) and assuming they have not gone past the nearest suitable then there probably shouldn't be an issue. (I think the actual requirement is that it can't be beyond the maximum diversion time or distance....)
Additional fuel ordered over flight plan fuel will in some cases change your ETOPS /DPA/CPE data. (Also depends on airport availability on certain routes)... It's just that many do not recalculate it.
Airmanship may ultimately dictate a different course of action.