From what I discern I believe it is possible Congress will block (or attempt to block) future Supreme Court Justice nominees. The shutdown to the process of confirming Merrick Garland is unprecedented, and at the time of this writing the process is stalled. Therefore I think it is likely such a technique might be used again by Congress if they are presented with a nominee from another Democratic president.
In the early 19th century, U.S. Supreme Court Chief Justice John Marshall authored the famous decision in Marbury v. Madison, which established the power of courts to review the constitutionality of statutes. Republicans argue that the U.S. Senate has the power to give its “advice and consent” regarding nominees. Yet the senator’s refusal to hold any hearings on the nomination does not meet that requirement.
No, if Hillary Clinton wins the election, Congress will likely vote on her nominee because it will be a different Congress. While the Presidential election gets the most press coverage, 88% of Congressional seats are up for election as well. A large turnout of Democrats to vote for Hillary is likely to vote more Democrats into Congress as well. Since most of the opposition to Merrick Garland comes from the Republican-led Congress, that opposition will fade once Republicans no longer control Congress. If Hillary wins, she can expect the cooperation of a Democrat-led Congress in confirming her nominee.
While refusing to vote on Judge Garland is a clear political stunt that will go down in history books as an supremely polarizing and divisive move, if they were to refuse to vote on Clinton's nominees, if she were to become president, it would trigger a constitutional crisis the country has never seen. A conflict that would require the intervention of the Supreme Court.