Personaly I DON'T think Imu will be defeated this arc, just pushed out for one or the other reason. He is supposed to be on some time limit after all. He may also be forced to retreat due to loss of one or two Knights *points to Sommers and Killingham*. Also honestly if we put into account all theories about Blackbeard trying to steal Imus power the BBG (big bad guy) on mural dosen't have to be Imu. It could be Blackbeard as well even though I really hate that idea. He's known from jumping people at their lowest to take from them what he needs after all.
They usually call him the opportunist.
Yeah, indeed B.B is a shitty opportunistic bastard BUT - Imu isnt some type of Old man dying with cancer - Imu is actually a IMMORTAL creature, surrounded by 17 of the STRONGEST army in the World (all Immortals btw) - all who can use WORDL FUCKING WEAPONS - all have OP fruits - and he is living inside a fucking fortress in the most high place of the world- thatnis being guarded by the FUXKING MARINES!!!!!!
I'll use Shanks own words- IF BlackBeard by some sort of miracle, can GET there, where his father got - even then - what the fuck he will do against this guy where he don't have any weaknesses (in M.G) has at least 4 forms - 19 weapons + Maki + strongest CoC in the series ?
If you count how many adversity is in the way to B.B accomplish this "goal" of him.. you'll know its IMPOSSIBLE !
And - i dont think even if B.B could defeat Imu in 1x1 (what is absolutely impossible, specially that B.B weakness are body harm, and Imu only do impaled moves ) I don't think B.B could master and awaken the O.G fruit, or even if he could use all this power - if every frut has a demon inside, the OG fruit for sure has the most powerful and big devil of them all !!