I totally understand where you are coming from and agree we can look clueless without him. The first half against Burnley being a prime example, he came on at half time and changed the game.
However, if we stick to this 433, which I really hope we do because we look unstoppable with it, then I think long term Gundogan will be an excellent long term replacement. He's not quite as good on the ball, but he's still a fine player and maybe could give us something slightly different, higher tempo, more energy, more aggression.
If you look at the Bayer Monchengladbach game at home it was 433 with DeBruyne and Gundogan as the number 8s and they looked fantastic together. That role is ideal for Gundogan.
On current form I can't see how you could possibly take Silva out of the side, he has been an absolute joy to watch this season and deserves player of the year so far. But long term I think Gundogan can be superb in the same role, although he'll play it slightly differently. Exciting times ahead!
Our team in 2 or 3 years could be:
..................Rulli
Maffeo...Tosin...Stones....Angelino
...............A. Garcia
.......DeBruyne....Gundogan
Sterling........Jesus.......Sané