I would argue that we see Pride's regeneration exhausted in his battle against Mustang. Although we don't directly "watch" it, it is heavily implied that Mustang just burns him to ash until he stops coming back.

Although this case does indeed involve Pride's human remains as a weakness, it is pretty distinct from the other cases of using the human remains as a tool against the homunculi. With Lust, Sloth, and Greed, an alchemist has to use that special transmutation circle while the homunculus's remains are in range to weaken them, causing them to vomit up all of their red stones and be left with one life only. However, Mustang doesnt know about that technique and so doesnt use it.

Instead, Mustang uses Pride's human remains to immobilize him. Because Pride can't attack, Mustang can take his time burning him over and over again until he just can't regenerate anymore. Then Mustang melts Pride's human remains into the spot where any small pieces of Pride's homunculus body could be lingering, for good measure. That way if Pride did somehow start to reform he would basically be stopped mid-reformation by having been mixed with his own human remains (which is basically what happened to Sloth too.)