If the democracts win in the midterms, does this mean impeachment for Trump?!

I don't think so. While they might be more support for impeachment with the addition of additional Democrats it can't be done without significant support from Republicans.

I just don't see it happening. The Russian "collusion" story is clearly not supported by the evidence found so far, and it seems like they are just throwing whatever they can at Trump and none of it is going anywhere.