I'm thinking they are going to need much more than what has been presented so far. Democrats may even themselves slow the process when they see Pence waiting in the wings.
They won't need more to charge or evidence to present. Existing cases already provide more than enough material for articles of impeachment. Remember, impeachment happens in congress, not in court. It's a political process, not a legal process. If the House impeaches and the Senate votes to confirm, there is no appeal to challenge the validity of the charging document. If the Senate votes to confirm, impeachment is a done deal.
What will have to change is the direction of the political winds. I believe that will happen as the various investigations continue to erode Trump's strength by bringing more and more truth to light, and as Trump responds in his typical self-harming ways.
The Democratic leadership is discouraging impeachment talk now because they know that impeachment talk will fire up Trump's base and encourage them to vote in the mid-terms. Trump knows this too which is why he's mentioning the impeachment threat in his rallies and other venues.
After the election, the Democrats will be more willing to beat the impeachment drum. They'd take Pence over Trump in an instant for a number of reasons, one of which will be intense pressure from the Democratic rank and file to impeach if they win the House.