This thread calls for speculation, so I'll throw one out there that I haven't really heard anyone suggest much...
Trump resigns and Pence pardons Trump and his whole gang.
I admit there are a few problems with this, one being that Trump would have to actually relinquish control, he strikes me as someone who would find that extremely difficult. Two, Pence was the head of the transition committee which is very much embroiled in a few of these Russian and fake Clinton email scandals, so it's hard to imagine his hands are completely clean. However, I think making a case against Pence is probably exponentially harder than Trump and many of the others, so my guess is that resignation followed by pardons would destroy most of the momentum of the criminal and impeachment cases that are being built. Three, this turn of events would play out much better for the Republicans if it could happen after the midterms, but they appear to have lost a lot of control and may not be able to choose their timeline; doing it before would just add additional momentum to the Democratic wave that is starting to build.
I've often wondered whether Trump will decide to 'take his ball and go home'. It seems like there are more days when he is mad/angry than days when he loves being president, and he's bemoaned semi-publicly how 'invasive' being president is. Only hurdle to him quitting is he loves the status too much, though he's certainly walked away from other things and declared himself "very smart - a winner!" by doing so. Shrug.
He might voluntarily go if he somehow thinks it would benefit him financially to no longer be Prez.
Honestly, if I were a GOP strategist I would at least spit-ball on ways to get DJT to voluntarily resign; in the meantime every GOP candidate is put in an awkward position where they can't offend DJT and risk his base turning against them, but to fully embrace him only works in very solidly red districts (and perhaps not even then - see Lamb and Jones - both of whom had no business winning in the districts they did on a more 'normal' cycle).
As for Pence pardoning Trump, presidential pardons only extend to federal crimes. Cohen (and - perhaps - himself by extension) are being investigated by NY. DC and MD are suing Trump over business violations. I'm amazed at the speed at which Mueller's investigation has progressed; we haven't even hit the 1 year mark, and already there is a slew of indictments and a few guilty pleas, and at least two warrant-raids. I expect charges on Cohen to come sometime in the next few weeks. Unless DJT is successful at stopping the investigation, Mueller might just file a very damning report a month or two before the midterms, though I'm speculating wildly on this last point... the Starr report only emerged 4 years after the initial investigation began.
Trump seems to particualrly blow a gasket anytime it emerges that his finances might be under scrutiny. Again, violation of state law wouldn't be covered, and perhaps there's stuff from any number of places he's done business (most notably NYC, but also NJ, Connecticut, California, Illinois, Virginia... not all of those have governors who would likely pardon him). What would/could he do if it turns out that Eric/Jr did more boneheaded, illegal and/or immoral things in pursuit of wealth?