No way is Blurred Lines going to decrease It's just starting to get featured on news media, and my frans are discovering it now too and they usually discover songs 1 year later.
APPLAUSE doesn't come out until 20 more days so there is still a chance that BL will start to decline before the single comes out.
But Robin has another version at #8 while the version at #1 hasn't decreased at all. He's selling almost 60% more than Miley, he could do around 450k this week with (literally) record airplay numbers that have yet to peak and will be even higher in four weeks. Nobody else can go #1 now