Another area of concern is a recent report by Merrill Lynch analyst John Murphy suggesting GM will lose more market share than it anticipates.

"We believe that GM's 18%-19% market share target is optimistic, and a more realistic range is 15%-16%," Murphy wrote. The projection was based on his comparative analysis of the percentage of new models in each automaker's sales, an area where GM ranks low.

However, GM spokesman Tom Wilkinson questions the metric's relevance. "We take a fairly dim view of that report," he says. "I don't think any legitimate statistician would look at that and reach the same conclusion."

Libby says GM is least likely to retain Pontiac customers who prefer performance vehicles like the G8 and the Solstice. Those buyers "will likely look at European products as well as Asian products with high performance," he says.

By contrast, owners of Pontiac SUVs, the G6 and the Grand Am will likely stay with GM, he says, because the purchases are not performance-oriented and buyers "are most likely connected to GM in some way."

Among GM brands, "Chevy is first in line" to gain Pontiac share, Toprak said. "Then come lesser brands, some Buick and some Cadillac. If GM is proactive in trying to keep those people and offers loyalty programs, the percentage will be high, over 50%."

In the worst-case scenario for GM, he says, Pontiac buyers will flee to Ford (F, news, msgs) because they feel "frustrated with the failure of old GM (and) they juxtapose that with the stability of Ford and its compelling lineup of cars."

The 2004 shutdown of Oldsmobile proves it can be done. "When they discontinued Oldsmobile, they were retaining most Olds owners, who were trading for another GM product," says Libby.

But Toprak says Olds shut down in an easier time, before GM's financial difficulties were so acute.

This article was reported by Ted Reed