You certainly can play without a target man. There's plenty of people who would rather we did I think, but I'm not sure we have the players to do it.
Most of our defenders aren't comfortable on the ball, so they end up playing quite a lot of long balls when under pressure. Without a target man that's going to mean the ball just comes straight back. Sigurdsson's strength is crossing the ball, and Klaassen's appears to be getting ahead of the striker into the box. Neither of which are massively useful without a striker playing with their back to goal. We also lack players who can pick passes from midfield, so if Sandro is going to play centrally I'm not sure who's going to be playing him in.
I think we'll be asking DCL to step up big time this year.