Independents went with Perot over his big issue, trade. Buchanan is anti-globalist. So, he had the "whole package" and could have won.
Even if one makes the (IMO) absurd assumption that Buchanan would have gotten *every* Dole vote and *every* Perot vote (adding up to 49.21% of the total vote) he would have gotten slightly fewer popular votes than Clinton (49.24%).
https://en.wikipedia.org/wiki/United_States_presidential_election,_1996
But in fact Buchanan could not possibly do so well. For one thing, many Perot voters supported Perot not on the basis of trade or any other particular issue but on the idea that we need a successful businessman in Washington to fix things--an appeal that Buchanan could not make. Second, not all Dole voters would support Buchanan by any means. By 2016 politics are so polarized that most (though not all) Republicans will vote for any Republican candidate but that was not the case to the same extent in 1996. Buchanan's staunch defense of World War II era isolationism and the background of some of his supporters would hurt him. They hurt him in the primaries btw. He only got 20.8% of the Republican primary vote (compared to Dole's 58.8%). Yes, he won the NH primary--*with 27% of the vote, worse than he got in the state in 1992!* This was his only primary victory in 1996, and it was due (apart from the support of the *Union-Leader*) to the divided nature of his opposition--Buchanan 27%, Dole 26%, Alexander 22%, Forbes 12%, etc. There is in fact no way Buchanan could have gotten the GOP nomination in 1996, once he had to face one-on-one opposition. And if he ran as a third party candidate, he would not have done much better than his 0.43% showing of 2000.
https://en.wikipedia.org/wiki/United_States_presidential_election,_2000 (Unless of course Powell was the GOP nominee, but even then I find it hard to believe Buchanan would get more than about five or six percent of the vote--though that would probably be enough to defeat Powell..)
1996 was simply not like 2016 (and Buchanan was no Trump). There was much less dissatisfaction with the economy (which is one reason Perot's vote dropped so much between 1992 and 1996). Republican voters were much less disenchanted with their party establishment. Appalachia was not yet in revolt against the Democrats--Clinton got more votes than Dole and Perot combined in West Virginia.
https://en.wikipedia.org/wiki/United_States_presidential_election_in_West_Virginia,_1996 In short, it was just not Pat Buchanan's year. (Not that I think there was ever a year he could win, but if there was, 1996 was not it.)
FWIW, the Gallup poll of February 1996 had Clinton beating Buchanan 59-35.
http://www.cnn.com/ALLPOLITICS/1996/polls/cnn.usa.gallup/022396.shtml#clinton.buchanan Now party loyalties being what they were (even in 1996, when they were less polarized than today) it would not have been *that* overwhelming (the same poll showed Clinton beating Dole by 56-40, whereas in the end he beat Dole by "only" eight percent ). But IMO the idea that Buchanan could have won either the GOP nomination or the election in 1996 shows a complete misreading of the politics of that year.