I feel like it would be fairly easy to leap backwards so long as your back isn't to a wall. The force of the leap alongside you yanking your sword backward should free it from most grips, I'd think. I'm just spitballing though, I've never actually tried to seriously grab any kind of thin blade, much less a fencing sword of some sort. I guess you could torque it in your grip to improve your control, I don't know how much of an effect this could have. I doubt it'd go much like the (fantastic) finale scenes of Rob Roy though, just because your asking your forearm muscles to combat a pretty hefty amount of momentum via mostly friction, which just isn't very likely to work imo.

Unless you had an equivalent amount of forward momentum yourself, coming in with a massive lunge to maintain distance against the retreating opponent. That's pretty all-or-nothing though. If instead of leaping backwards he moves into you, you have no cover (both of your hands are in use at this moment) against a potential fist or elbow to your face from his free arm, with the extra momentum of the two of you approaching each other.

By the way, I never thanked you for the corrections to my understanding, so thank you. This is admittedly not the first time I've had to take my spankings from an educated academic, I am a bit of a poster child for replica weapons being frequently inaccurate and thus teaching mistaken impressions. I do try to remember this, but it isn't always easy. I do have a strong appreciation for accurate understanding of history though, so thank you for taking the time to write up corrections and provide sources.