A semicolon in that position is very unusual and would seriously give the reader cause for pause, which may actually be exactly the writer's intent if it is being used as a creative literary device. But it is really non-standard and shouldn't be used for bureaucratic documents or the like. (And the construction 'semicolon-because-comma' is clearly wrong if you accept that anything can ever be 100% wrong.)
A semicolon can be seen as something between a colon and a full stop; the idea following the semi-colon is closely connected to the preceding idea, but at the same time it's an idea in its own right, so a comma may be too little. In fact in that last sentence a comma would be incorrect as there is no conjunction between the two main clauses.
But in your example there is another issue with the 'because' clause which is explained better than I can at the garden of phrases site. (My emphasis)
When an adverbial
comes later on in the sentence [...] the writer must determine if the
clause is essential to the meaning of the sentence or not. A "because
clause" can be particularly troublesome in this regard. In most
sentences, a "because clause" is essential to the meaning of the
sentence, and it will not be set off with a comma:
The Okies had to leave their farms in the midwest because the drought
conditions had ruined their farms.
This is the case with your sentence, so no comma -- and definitely no semi-colon -- is grammatically the best option.
For the sake of completeness, I'll add the remainder of the quote. It's about cases where the adverbial clause actually requires a comma.
Sometimes, though, the "because clause" must be set off with a comma
to avoid misreading:
I knew that President Nixon would resign that morning, because
my sister-in-law worked in the White House and she called me with the
Without that comma, the sentence says that Nixon's resignation was the
fault of my sister-in-law. Nixon did not resign because my
sister-in-law worked in the White House, so we set off that clause to
make the meaning clearly parenthetical.
Along this vein, in a tampered version of your second example there could be two separate meanings depending upon whether you use the comma or not.
He didn't drag me into his office because he needed to tell me something everyone should hear. (No! He dragged me into his office because he wanted to tell me something in private.)
He didn't drag me into his office, because he needed to tell me something everyone should hear. (He didn't drag me into his office. He publicly announced e.g. that the company was being taken over.)