So, am I getting this correctly:
For a full win, you need a nuke (to reveal the stairs to HF), invulnerability (to survive the blast) and the means to beat JC.
Stuff that can be used as a nuke: thermonuclear bomb, nuclear BFG, and Trigun.
The Spider's Lair has a guaranteed thermonuclear bomb, but the level itself isn't guaranteed. The Mortuary has a guaranteed nuclear BFG, and the level is guaranteed if you play on at least HNTR. The Trigun isn't guaranteed.
Stuff that makes you invulnerable: invulnerability globe, lava element.
Invulnerability globes aren't guaranteed. The lava element is guaranteed in the Lava Pits.
What you're saying is, a full win can be planned as long as you play on HNTR or up, visit the Lava Pits to get the lava element, visit the Mortuary to get the nuclear BFG, and survive to beat JC?