If Chelsea lost Costa for a significant period then it would impact quite severely - got a third of the league goals and a lot of them have been winning goals , he has been the form player , even when Chelsea were struggling to break down a team Costa has delivered with a goal to win the match or has made a match winning impact - he is the one player Chelsea can't afford to lose for any significant length of time. Kante would also be a massive miss .
But he's going to get some of those goals purely for the position he plays in, who's to say Hazard playing in that same position (as he has) wouldn't have got as many? Ok I accept he doesn't have the strength of Costa for some of those hard fought goals he's got but they'd be offset by different skills Hazard possesses.
I think we have a good deep squad who would step up and in quite well with any injury losses.