For several reasons I don't think so, but it is early yet.
The math is on the Democrats side, the Republicans have more seats up in states where they are more vulnerable.
There is talk that Trump could also really harm the chances of incumbents in these areas, while I can see an argument that the opposite is true, I think in Democratic states Trumps nomination just might spark fire in the bellies of Democratic voters go get out and vote, while diminishing the fire in the bellies of Conservative voters. Additionally, Election years are generally high voter turnout years...Republicans don't do as well in high turnout years. (Yes I know 12' was an election year, I said generally) Finally, even if Trump is headed toward a presidential win, I don't think his supporters will lock step vote Republican down ticket as they might if the top of the ticket was Rubio or Cruz. If Trump wins the General, it will because he attracted a lot of the more liberal middle, which might alienate some of the far right.
All in all, I think the Democrats gain seats in the 2016 Senate election.