The most likely scenario is Fedor zulu'ing Lesnar because Lesnar always tries to strike early on before going for a take down.
In his UFC debut, he jabbed Mir and then started going for take downs, in his fight against Herring, he went for a flying knee and then started going for take downs, in his bout with Couture he striked with him and then started clinching, in his fight with Mir, he dodged a few jabs and then took Mir down.
Brock Lesnar always tries to strike early on, but for some reason people think the first thing he does is go for take downs.
And with that being understood, standing with Fedor for any amount of time with the kind of crappy striking Lesnar has isn't a good idea- you're bound to get zulu'd.
People should also understand that Lesnar also has physical disadvantages, even though he's heralded for his athletic abilities people don't understand that his body build isn't good for striking. Sure his wide shoulders give him a great reach, but look at how slow he is.
Brock Lesnar's shoulders are too broad and his pecs are too developed to give him a good build for striking- if you watch him you'll see how awkward and uncoordinated he is when he boxes despite his tremendous punching power.
But assuming he does gets passed Fedor in the striking pocket, if he takes Fedor down there's also possibility of Mark Coleman like armbar where he is submitted instantly.
But that's not the likeliest thing to happen, and I think Lesnar's submission defense is highly developed enough to make him last.
Unfortunately, the reason he'll last is because he doesn't take too much chances with his Ground and Pound, securing Fedor to the 2nd round.
With every round resembling the 1st, it's likely Lesnar will eventually get KO'd in a 5 round fight.
Fedor via Zulu-like kulu in any of the 5 rounds.
Man, MMA fans suck at analyzing, everybody expecting Lesnar to (T)KO Fedor in a Mir-like fashion really missed out on spotting Lesnar's flaws.