You replace the elite goalscorer with a better footballer (not hard), and get an attacking unit of 3-4 players working together to get 30+ between them instead, adding variety and, crucially, consistency to your attacking play, because you can't be nullified by either shutting down the game of one player or if that player doesn't bother to turn up at all. Or, to be blunt, do what every top side does. If our aim is top four/titles, you don't do it through a player like Lukaku.
We won't push top four, mainly due to losing Barkley AND Lukaku in one go, so it'll take time to rebuild that attacking spine. But we wouldn't have done with Lukaku this year. The year after this we'll reap the fruits of aiming for a more balanced attacking unit.