Plus, it’s now impossible to say whether or not things played out in the same way for Reginald and Grace now that the finale has shown the present-day timeline to be completely different, what with Ben still being alive and leading a completely different team of children dubbed the Sparrows.
Conceivably, either the human Grace or the robot Grace could still be alive in the new timeline, though Reginald might not have had any reasons to build the Mom droid.
After all, Reginald clearly felt a certain kind of way about Grace considering he eventually recreated her as a robot mother to his non-biological children, even if viewers didn’t quite see THAT kind of devotion depicted.