British Airways will be resuming service from LHR to KEF on October 25, 2015. It will run W, F, and Su.

BA 800 LHR-KEF departs 11:20, arrives 14:35
BA 801 KEF-LHR departs 15:30, arrives 18:35

Getting back to the U.S. on the return requires an overnight layover in London, but you may find that preferable to flying AB's service to mainland Europe in the middle of the night.