With Bridgestone pulling out at the end of the season, it seems very likely that Michelin will return, however there could be other tyre manufactures joining them too - which to me is only a good thing.
http://www.autosport.com/news/report.php/id/82586
Could mix things up a bit
http://www.autosport.com/news/report.php/id/82586
Could mix things up a bit