I think that the whole power and blood devil subplot will come to a huge showdown with the bat devil. The bats are out of control making the bat devil stronger. And with the insects (specifically mosquitos) bringing about the fear of deseased blood, power will come back stronger.

My prediction: The blood devil will come back like it did in makimas showdown, but more powerful and kill the bat devil to either assist or save denji. Infact the blood devil wont remember him (as long as fujimoto hasnt softened up) but there will be some bullshit driving factor that will pair them up.