if you are going to stay, don't update to 8. Update to 9. Any 'significant' fixes you need fixed for 8 wont be possible in this stage of life and only 9 fits that requirement.
at this point, it will probably have to be a rebuild of a few machines - i'm not sure we can jump from 7->9 in an automated way (is it possible?) and i'm unsure how we'd recover if there was a hiccup in that process.
possible good news is that we'd been forced to use more machines a few years ago due to some IT policy about databases not being colocated on the same physical instance as the application(s) accessing it, which forced multiple servers when fewer were needed. I was told that's not a hard requirement any longer, which may allow us to consolidate some pieces during a rebuild.
I"m not sure how mature the LEAPP program is, but you could always simplify the process by running your apps in an el7 container for the initial migration while you ensure the rest of userspace catches up/adequately tested.
possible good news is that we'd been forced to use more machines a few years ago due to some IT policy about databases not being colocated on the same physical instance as the application(s) accessing it, which forced multiple servers when fewer were needed. I was told that's not a hard requirement any longer, which may allow us to consolidate some pieces during a rebuild.