| Quote #1
Now you have to live the rest of your life knowing you're going to die someday and disappear forever. (1.31)
This is Wade's philosophy. As someone who doesn't believe in organized religion, it makes sense that Wade is unconsciously searching for another form of immortality: heroism, which he finds online.
| Quote #2
A lich was an undead creature, usually an incredibly powerful wizard or king who had employed dark magic to bind his intellect to his own reanimated corpse, thus achieving a perverted form of immortality. (7.51)
The lich is also Halliday's "perverted form of immortality" because it was programmed by him and kind of acts like him. It's like a self-designed zombie.
| Quote #3
There was no such thing as a backup avatar. OASIS users could have only one avatar at a time. (7.54)
This is a plot gimmick to raise the stakes on the Hunt. If Parzival "dies," he has to restart at level one and lose everything. It's also a way that the OASIS mimics real life. You only have one identity, so be good to it.