I think things are going to unravel fairly quickly for Trump. I have no faith that Rosenstein (or Sessions) will appoint a special prosecutor or even bring charges when evidence is brought to the DoJ, initially.
But there are many threads of good circumstantial (at least) evidence that are being picked apart which will ultimately show shady business arrangements and collusion with the Russians by a large number of people. At some point the evidence will force Rosenstein's hand.
And / or state attorneys general will get involved in prosecuting Trump-adjacents for Russian money-laundering or racketeering that took place in their states and people will either flip or panic. With Trump being unable to pardon state prosecutions, these charges may help flip people. Flynn has already sought immunity for testimony. I would imagine Maniford, Giuliani, and Flynn would sell out absolutely anyone for a deal.
With rumors of grand juries being empaneled now, firing Comey is a panic move; so we're heading in the right direction.
As for what comes after Trump, I have no idea. Pence may not be clean, either, so we may have to work our way down the chain of command for someone clean enough to assume office. Maybe Kiefer Sutherland.