First of all, having a captive finance company didn't help certain stand-alone Mazda dealers early last year. Their captive, Ford Motor Credit Co., ejected them when it was short on funds during the credit crisis.
Then, take a look at Subaru dealers. They're thriving despite their lack of a captive. Their subvented loans and leases are funneled through Chase Auto Finance in a relationship that's similar to the one GM dealers now have with GMAC Financial Services, or Ally Bank.
If GM provides sufficient marketing funds to GMAC to support dealers with competitive finance and lease programs, and -- most important -- if it produces the right products for the times, GM will likely gain market share.
Of course, if GM doesn't, having a finance arm isn't going to save it.