That`s not entirely true, the cuban intervention in Chile went farther than the importation of a couple of sugar sacks...

There were some mercenaries and guerilla instructors involved, you know.
And the US sent military advisers, the CIA, weapons, School of the Americas graduates to Chile. The point was that the USSR and Cuba, while friendly to Allende's Chile did not control the government nor act as more than allies, which is more than can be said for the US. So the argument about keeping 'foreign influences out' is flat out wrong.

Do you actually believe that Allende`s people was just going to ship back to Cuba all the weapons, all the ammunitions, all the instructors, etc., should they have lost the plebiscite?

Do you think those would have been free elections?
How do you know he wouldn't. And in that case, had Allende lost the election, the people, with military support, could have legitimately overthrown Allende and put the proper democratic government in office. Thereby making Allende the villain for blocking democracy, as it stands he is the victim because he was the elected president.