For me, another striker is vital. I still believe that if Kane gets injured we are going to struggle.
It's not just the goals he contributes, it's the threat he carries. He is the number one target for any opposition defense, and occupies much of their time and thought. Whilst Son, Chadli, Alli, etc are all capable of adding goals for us, none carries the goal scoring potency of Kane.
I've always believed that you need as many attacking threats as possible to stretch and confuse opposition defenses. In an extreme example, look at Barca. There's Messi, Neymar, Suarez. While a defense is watching one or two of them, the other one is free to wreak havoc. In another example, Liverpool of a couple of seasons ago. Suarez & Sturridge. With Sterling causing additional problems.