To avoid follow on, Zimbabwe need 345 runs, which by itself is going to be a challenge. Zimbabwe had a good start yesterday, but surviving against Rashid Khan is going to be difficult from third day onwards. If Afghanistan could get the wickets of the experienced batsmen (Sean Williams and Sikandar Raza), then the remainder of Zimbabwe batting lineup will fall like a pack of cards. Probability is that Afghanistan will win this match, but let's see what is going to happen.
Zimbabwe is a far better team than Afghanistan. The problem with the Afgan team is that they are highly inconsistent, I do not think it will be a problem for Zimbabwe to reach 345 runs. They have started well and they will easily win this test too.
Not sure if Zimbabwe will lose by an innings as they will be taking their time batting to try and make Afghanistan bat again and maybe if they can get a small lead of say 100 runs, then it puts all the pressure back on Afghanistan to try and win the match. We don't see teams follow-on much anymore and to see Afghanistan ask Zimbabwe to follow-on shows that the Afghan team are confident they can get the job done and win the match.