The idea that you chuck on someone to get a goal is one of the old school British football mentality, it is very rarely effective. If Kane gets injured, we no doubt have a problem. Although it's still not a case of sacrificing games. It's not ideal, but Chadli and Lamela can play upfront at a push.
In terms of Kane not delivering for say 80 mins of a match, the kind of player Kane is, he's always more likely in my view to deliver in those last 10 minutes than any 'back-up' striker we might want to sign. You wouldn't take Kane off if you needed a goal in the last 10 would you? Anyway, we scored loads of late goals last season. Eriksen is the king of late goals