If someone casts Greater Magic Weapon or a similar weapon improving spell on a Soulknife's mind blade, does the spell persist after the mind blade dissipates (such as if it were thrown) and reforms? What if it is reshaped?
A mind blade is clearly a legal target for Greater Magic Weapon:
Powers or spells that upgrade weapons can be used on a mind blade
I just want to make sure it would actually be worth using, since I'd be likely to reform my mind blade fairly often.
Officially, no. When a mind blade “dissipates” it is no more, and any magic operating on it goes with it. Re-using form mind blade creates a wholly-new mind blade—see numerous references to creating “another” mind blade or “a new” mind blade in the form mind blade and shape mind blade abilities. In other words, a soulknife has an ability to create a mind blade, which is a weapon that can be targeted by magic. The soulknife does not get a special ability to store such magic or otherwise pass it from one mind blade to the next, and mind blades actually do go away rather than just retreating to some dormant state or something. Greater magic weapon targets a weapon, and soulknives get no special ability to allow it to target “their mind blade ability” or something—the rule is just that such spells can target “a mind blade” normally.
You could actually think of the greater magic weapon effect as a condition—similar to the broken condition that soulknives can explicitly wipe out by creating a new mind blade.
On the other hand, this is a completely unnecessary restriction, and I strongly recommend your GM houserule it to allow you to maintain such weapon buffs across multiple mind blades. I recommend this because the soulknife class is very, very weak—and I say that as someone who works with DSP. In fact, DSP intentionally designed the later soulknife archetypes—augmented blade, living legend, moonlight meditant, psychic armory, and war soul—to inject extra power in the class to try to compensate. Seeing as their entire schtick, even with the better ones, boils down to “I have a magic sword,” it just doesn’t seem appropriate to me to deny them (reasonable, efficient) access to “magic sword”-improving buffs.
It is also consistent with Psionics Augmented: Soulknife, which qualifies the mind blade by saying that magic weapon enhancements placed on the mind blade with enhanced mind blade share any daily pools from one mind blade to the next, to prevent souknives from getting infinite uses of such features. While Psionics Augmented: Soulknife does not address buffs placed on the mind blade, the exception I suggest for them seems consistent to me with what Psionics Augmented: Soulknife says.
I would, on the other hand, allow a soulknife to optionally fully reset their mind blade (excepting for limited-use properties, per Psionics Augmented: Soulknife), for example to remove debuffs from the blade, but it would be an all-or-nothing thing. I would allow this because, again, the soulknife is weak and could use the help, and also because so much of the soulknife is wrapped up in the mind blade and it is not appropriate for it to be trivially shut down. And, again, it is consistent: we know soulknives can explicitly use a new mind blade to obviate something breaking a previous one.