So here are Horford's numbers in the games that Embiid has missed that Horford has played.
10/26 - 23 p, 9 r, 5 a 50%
11/02 - 25 p, 5 r, 7 a 50%
11/04 - 32 p, 5 r, 4 a 65%
11/13 - 14 p, 8 r, 2 a 27.8%
12/07 - 8 p, 5 r, 3 a 75%
12/15 - 10 p, 9 r, 5 a 33.3%
12/31 - 5 p, 3 r, 2 a 16.7%
01/09 - 17 p, 8 r, 6 a 63.6%
The Sixers are 4-4 in those games, which is better then they fared last year without Embiid in the game. The next couple of weeks is where Horford gets a chance to prove his contract's value with Embiid going to be out. If he can keep playing like he has without Embiid (which is on the whole better than when they play together), then you see why the Sixers acquired him. They needed a guy to play when Embiid invariably missed games that could at least keep them floating. If Horford falters and can't do it and the Sixers go into the tank, then the Sixers chose the wrong free agent. Now is the time for Horford to step up and earn his keep.