Yes, but it is not automated. If you have bones controlled by IK, you can select them and key their rotation. This creates FK rotation keys using the rotation value that the IK calculated. These keys are applied and then overridden by the IK constraint, but if you delete the IK constraint or change it's mix to <100, then you'll see the rotation from the FK keys. You'll need to decide how often you want to set FK keys in your animation to get a reasonable approximation of the IK.
Like anything, there is of course overhead when using IK at runtime, but it is very unlikely to be a bottleneck. It's 2 dozen multiplies and a couple trig calls (sqrt, acos, atan2). About twice the work is done to solve IK if the parent IK bone has nonuniform scale, but even that is minimal compared to the other work done to apply an animation and pose a skeleton, and that entire amount of work is likely minimal compared to your application logic and rendering.
I'm not sure you'd see issues blending animations which mix IK and FK. You could use the Preview view for this.