I've had situations where opening fire on the engaging party has given me the window to cruise out.
I generally avoid shooting as there's an RP opportunity in every such encounter, but if the other side is uncooperative and just looking to score a kill, I do defend myself until I can get away.
Example:
Liberty Navy Capwhore: DROP THOSE TANKS THERE'S AN EMBARGO
Me: What, these? Fer personal use. Fights on Rochester're gettin rough.
Me: Y'know, I had a lotta trouble gettin' past Atka, lotsa pirates. You guys should patrol the Rheinla--
Liberty Navy: YOU HAVE FIVE SECONDS DROP THEM NOW
Me: ...y'know what? You need 'ta learn sympathy. I know a guy who knows a guy who can h--
BLAMBLAMBLAM
Generally, with luck I can escape with some hull left.
Question, though: Is this considered fleeing the engagement? Because while I'd stay off the lanes after such an encounter, I might not stay out of the system.