Would you destroy Caesar?

To kill or not to kill Caesar...hmm.

Well, as we see from history, the assassination of Caesar plays no important part in the dissolution of the Roman Republic (it was the mass political reforms Caesar instated, rather than his assassination, which lead to the coronation of Octavian Caesar as first emperor, though it could have been used as leverage for his campaign), save for a break between lifelong dictatorship and the Empire, via the Second Triumverate.  If one is to take the decision of assassination, one should consider when to do it.  When exactly did his reforms take place, what critical period could the assassination cause the prevention of the dictatorship of Caesar.

Alternatively, if you aren't going to follow that path, you have to question if the Republic has become dissatisfactory (as was one of Sulla's arguments, if I recollect correctly) in its dealings with the Mob, and also if the leaders are becoming incompetants.

Of course, this is from an objective view of history and not the "present."  It really depends on what time you are talking about -- is it just when he's gone into office as a lowly quaestor, or is it at the time just before he is about to leave for Gaul as a Consul to campaign to gain lands.  Is it as he returns with his men, crossing the Rubicon in a direct and vulgar disregard of political taboo, or is it in his early days, taking into account his uncle's direct conflict with Sulla.

I would say that if you wanted to preserve the Republic, he should be killed anywhen between his early days, to early Consulship.

If you wanted an Empire, just leave him to go as he will. 

Do you believe his assasination was the work of the pro-republic party or rather a plot (by Brutus?) to put someone else in Ceasers place?

Gaius Julius Caesar. He conquered Gaul, he conquered Pompey the Great in Italy, Spain and Greece, he quelled a rebellion in Egypt, he conquered most of Asia Minor. He was a spokesman for the Plebian, someone who's charismatic attitude won his support from Rome at it's core.

Caesar was a hero, not a villian, and I would more than gladly follow him into wars, physical or political. Hail Caesar.