Dana White has said over the last few days that there is a "very, very, very good chance" that Brock Lesnar will be back with the UFC. Whether that is as a full time fighter or not remains to be seen. But with Lesnar meeting with White over the weekend, speculation is beginning to increase that the Beast will have some sort of commitment with the UFC after WrestleMania.
For me, I think he's going to try and wrangle a deal for himself much like the one he has now. He'll be a WWE wrestler some of the year and will probably get one or two fights with the UFC too. I think that suits everyone the best but there's a lot of organisation that goes along with that. I think everyone is keen to get a slice of the Lesnar pie but money always talks and Lesnar is a business man at heart.
I still think he stays with the WWE after Mania. His schedule will likely be reduced with the WWE after he loses the championship, so he'll be free to do whatever he wants in his spare time.