Biscotti has historically given Harbaugh the benefit of the doubt when it comes to injuries. And the Ravens have had sooooo many injuries over the past several seasons. They lead the league in starters on injured reserve IIRC.
Flacco and Harbaugh will always have a combined legacy. All you have to do is take a look at the contract situation to understand why the Ravens make the decision to keep Flacco and Harbaugh.
First, Harbaugh is is signed through 2019. The common thread is for coaches to get fired early in the offseason ("Black Monday") the offseason before their final contract year. That means Harbaugh can be expected to last through 2018.
Flacco is a whole other beast. The Ravens cannot cut him in 2018 because he'd represent a $4,000,000 salary cap deficit in a season where the Ravens are expected to be tight against the cap. That's $28.7m in dead cap if he were cut in 2018, if you were wondering. Flacco cannot be cut before 2019. In 2019 he would represent around 16m in dead cap but a whopping $10m in cap savings in 2019. The Ravens would be on the hook for another $8m in 2020 if they cut Flacco in 2019.
Harbaugh and Flacco are here to stay through 2019. Marty Mornhinweg isn't long for the world. If he's fired this season he'll be replaced by Greg Roman in the interim and followed by Bruce Arians, Roman, or another top three available OC that runs an Air Coryell or West Coast offense with some reliability.