If he is Mera Mera user, guy at the bottom panel wouldn't say: "Corazon is burining"
When we come to him, some possibilities are:
1. Corazon sacrificed his life to grant Law an immortal life span, since the latter was dying due to some illness.
2. Corazon gave the Ope Ope Fruit to Law, which allowed the latter to heal himself by normal abilities of the Ope Ope Fruit- but Doflamingo killed Corazon for giving him such a valuable possession.
3. Corazon ate it himself and healed Law using normal abilities from the Ope Ope Fruit, but again Doflamingo killed Corazon for eating what is a very valuable Fruit to the Donquixote Pirates.
It was stated that Doflamingo killed Corazon, so it's unlikely the latter sacrificed himself to use the immortality ability of the Ope Ope Fruit. That is unless the sacrifice itself isn't sacrificing your life immediately, but is something that greatly shortens your life span or something to that effect, and then Doflamingo killed Corazon before the latter could die "naturally".