I think it will be a challenge between him and Djoker realistically dex. Fed well lose points because I don't see him winning anything from now until year end.
People said the same last year after he slipped to #4 and look what happened.
I don't see Federer winning all three tournaments again (although I would never rule it out) but I do think he will win at least one or two of the last three tournaments.
I don't think Murray getting to #2 by the year end is that realistic in all honesty, short of dominating the last three tournaments and hoping for Federer not to win any. A 1700 point swing (which is how far behind Murray is in the YTD rankings) is just too big in all reality.