3 months after lipo /fat transfer I start to smoke marijuana. Can my cells die?

Thanks for the question. I suggest you should meet your Board Certified Surgeon to talk this situation. Because it's better to wait a couple of months, your operation area trying to get healed. Then after yes, you can do smoke and drink. I wish you all the best.

While most surgeons wouldn't support your use of marijuana, smoking it should not have any effect on your surgery at this point in time. Grafted fat that has survived three months is no longer fragile enough to be damaged by marijuana smoke. 

With fat transfer, 30 to 50 percent of the fat that was injected will not survive so you can expect this decrease in size that you have experienced.  As for smoking marijuana, I do not think their is any proof that it causes a reduction in transferred fat cells.