I haven't yet watched the video to avoid it taking any influence on my response. I am going to watch it after posting here.
I suppose the time of his assassination would play some role "before coming to power" would probably mean an assassination before 1933, but given that when calling a killing an asassination it suggests that the dead person probably would be in the public spotlight already (rather than for example a largely anonymous Hitler being killed in WW1). So assuming that he would be killed prior to 1933 but after getting some public attention for his attempted putsch in 1923 Hitler still might have inspired some misery in case whoever would have taken power would have taken Hitler's book "Mein Kampf" literally, a book which Hitler wrote in arrest after the failed putsch and which leaves little doubt about what Hitler was up to.
The overall situation of Germany in the 1920s and 1930s made the country a real brooding pit for radical nutcases. Dissatisfaction with the democracy of the Weimar republic, discordance among the many small political parties (not all of which were radical), the anger about the treaty of Versailles, the high rate of unemployment and economic suffering (especially after the crisis of 1929) and the fierce and violent battling between radical factions of the left and right wings made it very likely for somebody to seize dictatorial power in Germany, since large parts of the population were willing to let this happen. I'll therefor base my scenarios on the presumption that somebody else would have ended up with dictatorial powers rather than the pretier scenario of a continuation and growing acceptance of democracy in Germany at the time.
Antisemitism was regretably present among many Germans, with or without Hitler, but still chances are that not every dictator which might have come to power would have been as ready to carry out the madness Hitler had laid out in "Mein Kampf". The breaking out of another war was likely (though not set in stone) even with a different radical than Hitler in power. The horrible crime of the Holocaust may perhaps not have been as likely under a different dictator.
I guess the worst case scenario would have been a different dictator who took Hitler (based on his writings) as an example to follow but who was a better strategist than Hitler. The worst case scenario would be a dictator who in many ways (especially in his persecution of war and genocide of the Jews) would resemble Hitler, but on the other hand would not have made the kind of decisions Hitler made which contributed to his failure (such as the bombing of towns rather than airfields and military facilities during the battle of Britain, the decision to attack the Soviet Union, the many orders prohibiting any kind of tactical withdrawl, the decision to turn the Me-262 into a bomber etc.). Probably the best case scenario short of a lasting of the democracy in Germany would have been a moderate dictator at the time. A dictator that is who didn't share the fanatism (especially the antisemitism) of Hitler, who would have focused on the country rather than personal interests and who would have been ready to give up power when it was no longer helping the country. While such a "lovely, kind, dictator" sounds very fictional, there is actually a contemporary at the time whom I was thinking of. Mustafa Kemal, better known as Atat¸rk (which means "father of the Turks") came to power through a putsch similar to the way other dictators did. Throughout his rule over what remained of the former Ottoman Empire he made a number of decisions he could not have made without the dictatorial power he held. The forced deportation of the Pontic Greeks (combined with the Greek decision to force Turks living in Greek to settle in Turkey), and his harsh punishments of people who ignored his prohibition of the continuation of a number of Ottomanic traditions are among his harshest decisions. Given the context however these decisions may have helped to prevent future wars and conflicts. Atat¸rk transformed a weak and defeated, backwards oriented country into a modern nation and did reestablish democracy (though to this day the military which brought him to power does play a very important political role in Turkey) even at the risk of giving up his power.
A dictator of similar nature in Germany at the time might have taken some measures similar to some Hitler took in the 1930s, perhaps the unification with Austria (which most Austrians were quite happy with at the time) might have been conducted by such a dictator too. However, in case of such a dictator it would not have all been work in preparation for a future war but more on behalf of reestablishing Germany (especially in the mind of the people at the time) after the defeat in WW1. Such a dictator would not have striven for conquest of further land or reoccupation of territories lost in WW1 (Mustafa Kemal never tried to reconquer the former Ottoman territories which became independent after WW1 either), but rather would have tried to consolidate Germany by non-military means and reintroduce democracy at a time when people were more accepting for it.
PS: Note that I am not speaking out for any kind of dictatorship with the second scenario I described. It was a "best case" short of a continuation of democracy scenario.