Having removed Trump from the ballot, the Illinois Electors will not be seated in the electoral college when it gathers in December.
That will be true only if the Republicans hold the House of Representatives. The new (118th) Congress will be sworn in January 3, 2025. If the Dems win the House, that strategy is dead.
That's not how the electoral college works. The electoral college does not meet in one location, hence they could not be denied any seats. If Trump were kept off the ballot in Illinois, Biden would win the electors, who would meet in Springfield to cast their votes which would then be sent to Congress. If the GOP holds a majority in Congress (both houses), they could vote to refuse to accept those electoral votes, but that is not automatic.