Since we are talking about a situation where you cannot just look up the allowable span for an 8"x8" solid oak girder in the IRC, you need an engineer to answer your question. Anyone else is just guessing.

Option 1 - hire an engineer to look at it and either say it is ok as is, or to design necessary repairs.

Option 2 - hire a contractor to install a new column and a proper footing, and take your chances.

Option 3 - Do nothing and take your chances.

Keep in mind that many structural failures with wood do not occur quickly, which means an over-spanned beam will not necessarily snap in two the moment a support column is lost, and send the house crashing down. It can happen slowly over a period of many years -- the wood bends and flows as the stress of the load is placed upon it.