If I inject 1000cc in each butt cheek how many ccs will remain over time?

 Indeed you are on the right track by wanting buttock implants because they will be permanent as opposed to fat grafting which is extremely unpredictable amd unreliable. If it is 1000 ccs of fat that you have already had injected, nobody knows exactly how much will remain, but it is likely to be less than 200 ccs and even more likely you will be disappointed with the final result after a year or so. On the other hand, FDA approved buttock implant volume results are much more predictable and reliable because the implant does NOT melt away and cannot rupture or leak. Glad to help. 

After an initial loss phase, 50 - 60% of the fat injected becomes vascularized and obtains permanence as living tissue. Implants should be placed within the muscles for better long term results. The key to this surgery is to select an implant that is not so large that the muscle cannot cover it reliably. You want a nice result, but you want to avoid the complications (need for removal, infection, extrusion, fluid collection, implant migration, implant visibility, and capsular contracture among others). Studies have demonstrated that sizes above 350 cc have a greater rate of complications.  For those patients who desire more volume, buttock implants and fat transfer to the buttocks can be combined.Kenneth Hughes, MD, Board Certified Plastic SurgeonLos Angeles, CA