Personally I think, at this point, Mueller's entire investigation is meaningless. Whether President Trump gets impeached or not, is going to come down to one thing, and one thing only, which party controls the House after the next election...
Or to put it another way, even if Mueller would clear President Trump of all wrongdoing, a Democrat House is still going to impeach him, even if it's some bogus and meaningless charge like "racism". And on the flip side, even if Mueller presented a laundry list of wrongdoing, a Republican house is going to say, thanks Bobby Boy and file away the report in file 13.
Mueller won’t finish until after the November election. He’s waiting to see if the democrats gain the house so that they can start impeachment. If the House doesn’t flip, then he’ll end his investigation.