**GUESS WHAT? MORE SPOILERS!**
There are possibilities. Doc can create more clones of Hank and Dean, ya know. With all the technology he's got (and the greater technologies that J.J. created), he can pull it off without a hitch. Plus, I'm pretty sure Doc can rebuild HELPeR. He's rebuilt him times before. Like the time HELPeR was beheaded when the Guild invaded the Venture Compound. A few episodes later, he's good as new. Plus, There is the possibility that 24 can be brought back to life, if Dr. Venture would make a compromise with 21 to let the latter make a duplicate of 24 (or ask the Monarch to do it instead). Also, I don't think Molotov and the Blackhearts are going to be the villians of next season. After all, they did thank Brock for killing "the competition".
As for Brock, he may find a job elsewhere, like working for Jonas Venture Jr. or like you said, joining Molotov's Blackhearts. Hatred, however, will most likely end up with the OSI (again) and be Venture's replacement bodyguardfor Brock, while the Monarch will take the role of Dr. Venture's archenemy, in place of Hatred. But what bugs me is this: why the hell did the Phantom Limb only show up ONCE this season? I hope the fourth season covers more on the Phantom Limb's whereabouts, as well as many more mysteries, including the ones I just mentioned above.