I guess the big factor is how they're planning to line up. Are they gonna use Pedro/Sanchez up top with Messi and Neymar or are gonna have iniesta/fabregas in the wide attacking spot with the other playing just behind messi. If so then it's highly likely that Thiago this season and certainly next season would get increasing game time in Xavi's role. If they are planning on using pedro/sanchez as big members of the squad then Thiago has an issue as that's a lot of players for only a few variable spots in the team.
If they did convince him that he would get more time I guess this season if he really wants to go to the world cup he'd have to go on loan somewhere. The problem is that his choices would be limited. He'd need regular football at a top level club with CL football but the problem is the biggest clubs surely wouldn't want to loan a player like that but would want to instead develop their own player/integrate a new player.
So short term he's got an issue, long term though, even starting from the 14/15 season you'd think his chances of getting in the Spanish team would be better regularly playing for the top spanish team with busquets, iniesta, fabregas if that is really a big reason in why he's thinking of leaving.
It's sad but I think considering that its only really one season before he should be able to become a regular in the team that, that has to play a part in his thinking. If he leaves there's still no guarantee he'll make the world cup squad, if he stays though than sooner rather than later he will come in for xavi, playing for the number 1 team in his home country, unless they have another player in mind in which case you'd think they wouldn't be so fussed about loosing him aside from the potential loss in transfer fee.
I hope he comes but at the same time you can see that there's a lot to be said that a little patience and he could be part of their first 11 by the end of the season, but then you look at Martinez and if he did leave for us he could be a key member of an equally big club straight away. There's a lot to think about, guess we can only hope. Who know's may be the door might open for fabregas who might turn out to be the one that they just can't fit in.