Where my dorsal hump used to be is now very soft and squishy. I am worried about a possible development of inverted V deformity

I do not know how long ago you had your rhinoplasty, but if it is within the first two to three weeks, my first instinct is to rule out a fluid collection or hematoma beneath the skin. I have seen this on a number of occasions over the bridge of the nose and it feels soft and "squishy" as you describe. A small less than 1 cm fluid accumulation can be causing that which can be easily aspirated with a syringe while you're awake in the clinic. However, if this proves not to be the case, this soft spot can be representing edema or swelling  (which will go away on its own)  or a discontinuous transition from the nasal bone into the lower part of your septum and nasal tip.  This would not necessarily represent an "open roof" deformity put more likely a saddle nose deformity which could be very minor or more significant. I suggest you follow up with  your plastic surgeon to get further details and reassurance.

Mckenzie, I guess the better question is when was your surgery done? If there was extensive dorsal work, then it can be expected for there to be soft tissue swelling. To a certain extent, different parts of the nose swell differently and at different rates.  The reason for that is that not all of the skin over the nose is uniform - the nasal tip, for example, as it swells can feel rock hard.  Whereas the nasal dorsum can feel like a sponge.  The best gauge of how things will heal once the process is completed is how your nose looked immediately after the cast was removed.  Remember, it can take a few months (between 3-4) for the majority of the swelling to come down, and a total year before you see the final result.  When in doubt, contact your PS's office with any concerns, or bring them up at your next post operative visit.  Best of luck.  Enjoy your new nose!

Sounds like you are very very early in healing phase! Best to allow at least 3 months healing before seeking opinions of the appearances.