Lee's Survival (Hypothetical)
The following is most likely old news, but as a courtesy, there are a few potential spoilers.
To begin with, just to make sure no one gets the wrong idea, I'm not suggesting that Lee survived the end of the 1st season, nor am I suggesting that he should have. His death marked the perfect ending to a great story. That being said, the following is simply my own idea behind a hypothetical scenario in which he did in fact survive the season 1 finale. How you may ask? Well I've put some thought into this little bit of wishful thinking (and that's all it is). Anyone reading is free to disagree with whatever points I bring up or to point out any flaws in the logic behind any of it. I think it's fairly air tight, but I could easily be wrong.
In order to all a level of plausibility to Lee's survival, certain conditions would have to be met in terms of player choices, and a few established events have to be edited slightly, though not completely altered. To start with, the only way for Lee to survive the bite is if the player chooses to amputate his arm, but when that happens, it can't be Lee himself who cuts it. From that point, episode 5 plays out exactly the same up until his final scene with Clementine. In my version however, Lee's declining physical condition is not a result of infection, but actual sickness similar to Rick Grimes shortly after the death of Lori and Judith (blood loss, stress, fever, health hazards abound). Since the timing of these symptoms coincide with his having been bitten, he merely assumes that he's going to turn, which is why he has the option to tell Clem to shoot him. To explain why the walkers apparently couldn't distinguish him from other walkers, it seems possible to me that the amount of blood left on his clothes from the walkers he killed getting into the Marsh House could have theoretically been enough to mask his scent. As the season draws to a close, Lee still appears to die, but in my version has merely fainted (as he had a habit of doing at various points). And rather than Clem actually shooting him, the season cuts to black after she picks up the gun and points it (the implication being well established).
From this point on, Lee's continued survival takes place during a dlc in the same vein as 400 Days, which depicts 6 days of his life at different points between the 1st season finale to at least the first 3 episodes of the 2nd season (no accounting for episodes 4 and 5 yet). We open to Clem pointing the gun at Lee, but showing that she can't bring herself to shoot him, no matter what he told her. While not technically a retcon, her feelings of guilt that she expressed later on could stem from her having failed to put Lee out of his misery.
Cut to some time later where Lee wakes up, alive, and in poor condition (better than he was, but still). The blood from his clothes is fresh enough that he's gone unnoticed by any walkers that might've made their way into the store. Since he's still handcuffed, he manages to break his thumb to slip out (someone correct me if that doesn't work. Sources vary). Remembering what he had told Clementine, he builds up enough strength to try to find her, heads for wherever the player had him send her, but can't quite make it. Hearing the sound of bells, he blends in with a herd of walkers towards what he hopes is Molly. Depending on prior choices, assuming neither Lee nor Clementine failed to save her in Crawford, we meet up with her again. She manages to find some medical supplies to help him, but recovery takes a week or two of hiding out. Once Lee is strong enough to move, he has the option to convince Molly to go with him. If he chooses any dialogue option that doesn't involve Clementine, she'll stay in Crawford. By the time Lee and Molly make it to where Clementine would've been, she's already moved on. This doesn't stop Lee from following any and all leads towards finding her that he can.
Each proceeding episode of the dlc would then go on to involve Lee encountering new characters and being given the option to let them join them (assuming Molly doesn't die, which may be an option). In some cases he'll have to choose between two, in some he'll have to decide whether or not to kill them, and some may just die between segments. All the while Lee would struggle with the possibility that Clementine might be dead, and what, if not her, he has left to fight for. By the end however, once he's nearly lost all hope, Lee will hear rumors about Wellington, and decide it's his last, best shot to find Clementine.
Just to clarify, Lee and Clementine Never find each other again, whether that means either of them die for real at some point, or are seperated permanently (that'd make for some interesting game options). Since both characters often acted as accessories to the other, it's gratifying to see Clementine develop independently from Lee in the 2nd season, and I like the idea of giving Lee that same opportunity. This way neither of them know for certain if the other is alive or dead. Clem would be the one trying to move forward leaving the past behind her, while Lee would be the one clinging to the faint hope that he can reclaim the one piece of his past he couldn't afford to lose. Since I don't know how season 2 ends, I can't speculate as to how any of what I've written would translate into further installments.