you seem to be labouring under some conspiracy theory delusion.
If there is a four-way final, the public will have about half an hour to vote in an interlude before the second half of the program.
This year a four-way final seems unlikely due to the dropout, so it should be a four-way semi-final... or not?

Hell no.

I doubt there will be a four way semi or final, with the drop outs as has been said. They have done it before with 3 in the semi. Then use loads of filler to hit run time.

If he makes it to the final 4 it will very much depend on how they score people.

No tied scores to start with.

Then top place needs to be the third most popular, with second place the second most popular.

Creating
Judges Public Total
......4............2...........6
......3............3...........6
......2.............1...........3} Dance off
Ed.1.............4...........5} Dance off

There is only 3 in the final week which gives the judges slightly more control at the quarter & semi final stages.