Personally it would kill all the mystic and momentum of his return for him to be eliminated at the Royal Rumble. All this build up to it and for him to just be thrown over the top rope, as just another wrestler. I can only see two ways of this turning out;
Logical Idea - Jericho wining the Rumble in a unique way (Number 30# Eliminating no-one to win etc.) is the only way it would tie in. People suggesting he will interfere in the World Title match, I'm not as sure, why would he enter the Rumble if he planed on getting involved in the title match. Again the only way it would tie in is if the Title match is after the Rumble, and Jericho wins the Rumble. The Rumble now appears to be key of his return (All the highlights he showed on RAW last night, it was the best of Jericho's career in the WWE; Feuds, Titles, WrestleMania Main Event, Undisputed Champion, Tag Champ, IC Champ....EVERYTHING possible to achieve in the WWE, apart from winning the Royal Rumble!). I think yes it's getting predictable that he is going to win it, but they way in which he will win it won't be predicable...
Long Shot Idea - One other way of looking at it is this year the WWE is pushing that ANY wrestler can enter the Rumble even if they have had a match before hand (Tho this has always been the case, the WWE is mentioning quite a bit, which makes me think it's key to this years Rumble outcome). Jericho could be the last man in the ring and awaiting number #30, which would be CM Punk. POW Feud....but this goes against the slow build and without any explanation from Jericho before RR, it wouldn't make sense to the average WWE fan, only the IWC. So this is why I think it's a long shot.