The U.S. Constitution states
The Vice President of the United States shall be President of the Senate, but shall have no Vote, unless they be equally divided.
I understand that if a Senator's vote is "Present" then it counts as a "No" in the tally, but what if the Senator doesn't attend the vote. There are votes in the Senate Vote tallys that do not add up to 100 votes, so it has happened in the past.
Vote Counts: YEAs 56 NAYs 39 Not Voting 5
Since this vote is not "equally divided" would the Vice President be able to vote (if it was 49-50).
Has this been under judicial review in the past?
If a Senator missed a vote (deliberately or not), and all other Senators are present and voting, it would deny the VP the opportunity to break a tie. However, there's no point to deliberately doing this.
In other words, choosing not to vote can only make a difference if the VP and Senator agree, and can only result in making the Senator sad. There is no scenario where the Senator is better off by not voting.
A US senator cannot guarantee that the vice president won't be able to vote by staying away from the chamber, because there is no way to guarantee that another senator or senators might also refrain from voting, resulting in a 49-49 tie (or indeed any smaller number of votes, evenly split), whereupon the vice president would be able to vote.
The only way a single senator could definitively determine whether the vice president could vote is to be the last senator to vote, when there have been an odd number of votes cast, with one more vote cast one way than the other, or there have been an even number of votes cast, equally split.
It wouldn't block anything even if they did so.
According to this Wikipedia table, there have been cases where the Vice President has voted when the vote was tied 49-49 (or even as low as 46-46), resulting in a 50-49 (or 47-46) vote which passed the bill. But a bill would also pass if the vote was 50-49 without the VP voting. You need a majority of Senators present, not a majority of total Senators, voting in favor.
If not just one, but all 50 Senators that were against the bill were absent, there could be a lack of quorum (the other 50 Senators would not quite be the "majority" needed, and the Vice President is not a Senator so he doesn't count towards the quorum). But the Senate rules (and Article I Section 5 of the Constitution) say that members may be compelled to attend if a quorum is not present.
Can a U.S. Senator block the Vice President from voting by not attending a vote and having the results be 49-50?
YES, but it won't help their position if they're in favor, or opposed to it and their own vote would split the decision in either case. Either the "non-voting" senator's vote is moot (49-51 / 51-49) or it would split it forcing the VP to vote. Majority wins the day either way. So by not voting he would block the VP from voting but whatever the 50 vote was in a 49-50 or 50-49 vote, it would be the victor. (Hopefully that's what they'd want) In either case, this vote would go to the president's desk for veto or approval. So unless you were trying to save face for the VP by not making his position on a matter public, or your vote wouldn't matter, there's no reason to NEED to "block" the VP's vote. It won't help your cause.
For those asking is 50 enough or is 51 enough, you only need majority to go to the president's desk. If you have 2/3s majority (67 votes of 100) then it won't even grace the president's desk, it'll be considered law after that and in that case the VP wouldn't vote anyway. That's the only way to stop the president from having a decision in the vote.