Just to add to what Homer said, when Paul closes out the resurrection theme at vs. 58 it seems that his conclusion is that our present walk with the Lord, our dutifulness and faithfulness and perseverance, is tied to the expected reward:
“Therefore, my beloved brethren, be steadfast, immovable, always abounding in the work of the Lord, knowing that your labor is not in vain in the Lord.” NKJV
The reality is, I think, that since we have been made in God’s image and, therefore, possess certain characteristics given to us by Him in creation, and because He is the God that He has revealed Himself to be, it becomes almost impossible to do anything but speculate on this question.
I agree with Steve in this sense, that if God, being the same God that we know Him to be, were to have devised a different purpose or plan or whatever for us, then our duty and privilege, would still be to serve Him and glorify Him as best we could.
But I think that what Paul is arguing in vss. 12-19 is that, included in the proclamation of the gospel, is the testimony that God raised Jesus from the dead. Now, if in fact, God did not raise Jesus from the dead, that would call into question everything we know about God. God would be shown to be a liar and His character would be greatly impugned. And in this circumstance, we might as well eat, drink and be merry, etc. because how could we trust anything God says. We certainly couldn’t have much hope in our being resurrected.
So when Paul says, “If the dead do not rise” or “what advantage is it to me, if the dead do not rise”, in my opinion, he’s not alluding to some alternative plan that the God we know from scripture chose to accomplish, instead of the plan He did accomplish, but rather he is pointing out the foolishness of following a “god” which, in this case, would be the antithesis of the God which we find revealed in the scriptures.
If God were not to be the God He has revealed Himself to be, then who's to know how different our natures would be and in what manner we would or could respond to this "different" God?
It does seem, however, that in verse 58 Paul is dangling a carrot in front of us…

l2j