Restylane can be used following fat transfer. However, in the ideal situation you would not need any additional volume. However, Restylane will allow any irregularities to be covered up or smoothed out while you heal. Since you're three months beyond surgery, I would not expect your fat transfer...
I don't see a need for additional hyaluronidase at this time. I suggest you be evaluated and then wait for the lower eyelids to recover. You may need to have a procedure to tighten the eyelid skin or a blepharoplasty to remove excess.
Some people do experience unwanted side effects after these procedures. The reason for the droopy eyelid is usually when botox is injected above the brow. You might have a low brow or excess skin on the eyelid and once the brow muscle relaxes, it can drop a little causing the appearance of the...