I also remember the rumor of Michelin sticking around with Ducati. But the SNS were gone in 2008 because of the tire allocation regulations, not because of cost. Cost was a factor in the rule, and you may be right that Michelin couldn't afford to do it anymore, but the rules outlawed them anyway.
Hmmmm. I think if you take a look at the nasty old corporate world michelin's withdrawal from motoGp was just part of terminating a fringe marketing strategy. Before they left MotoGp michelin had already pulled out of F1. Since leaving the 2 top levels of motorsport their profits have increased by around 90% (not just from saving on motorsport spending) and they have acheived high sales growth rates in the heavy truck segment - not sportsbikes and cars. ImO the glamour of MotoGp and F1 was something that was just costing money and didn't fit into their longer term business strategy. I do believe that it would be better for MotoGp if we had more variety - including tires - on the grid. If somebody wants to spend the money on SNS - then so be it - less rules and more racing.