Your image might not develop at all. If your developer has been contaminated by fixer you should discard the solution and mix up fresh before developing your film. Fixer is acid. Developer is alkaline. All other things aside, the acid in fixer will neutralize at least some of the alkali in developer, causing the developer to slow down or stop working altogether. Your image would either be underdeveloped (at best) or not developed at all.
As an aside, one reason for using a mildly acid stop bath between the developer and the fixer is to neutralize the alkali in the developer before it's carried into the fixer. This will make your fixing bath last longer.