Delete index while query is running, is it possible?
Yes, a plain INSERT is fastest when no indexes have to be maintained. So it may pay to drop indexes before huge bulk inserts and add them later. Depends on the whole situation, of course.

No, you cannot drop a PK or a UNIQUE constraint or even a plain index in the middle of an INSERT, which also writes to the index.

No, I don't think your query should take more than three days, even if you import every link that every Wikipedia site on earth ever had to offer. There is probably something less than ideal in your command or setup or hardware or how you read / write the data.
For starters, an operation of that magnitude would rather use COPY:


Increased performance from single statement, multiple row inserts?