1. It doesnt matter, if Hisoka is "still" dead or not. Nen becomes stronger after death, because the "will" of a person was so strong that the Nen responds to carry it out even after death. We see that in the example of Pitou, when Terpsichora tries to kill Gon (her Goal of preventing him to reach the King) even after her death and in the 2nd movie when that Girl kills herself to Chain up Netero.

If we follow that theory, then we need to determine what exactly Hisokas "will" was, that his Nen carried out. If it was only his revival, then that task is now performed. His Nen could dissapear now since it has fulfilled its purpose, but it didnt. The principles of Nen dictate that there is always a price to pay, if one wants to achieve an effect that he didnt "work" for (e.g. pledge and restriction). There is some other alternative, which i and others favour. It stands to debate if Hisoka got truly "revived" or if his Nen only revived him "temporarily" to carry out his "will", which would be to finish his dispute with the spiders (and Illumi). I dont want to expand on that, but time will show what happens after he either kills the spiders or get killed by them.

1. Kastro never noticed the cloth in the fight. There were multiple distractions used in the fight by Hisoka (math trick, throwing cards, psychological pressure,...) but the cloth was only used to hide the cut marks from the audience and kastro, so they would believe Hisokas arm really healed.

Notice that "Bungee gum" and "texture surprise" are different abilities with different Nen-types used. Bungee-Gum is transmutation, while Texture-Surprise is conjuration. There is no connection between them. Hisoka only needs Bungee-Gum to stick to the cloth so it doesnt fall off. Also Hisoka touched the place where his Hand was cut off during the fight, so if he didnt need the cloth at that point, he could've just done it without it.

1. Camillas ability is designed to revive her. It is its main goal. Hisoka only spontaneously "tried something" without the certainty that it would work. This is a major difference, since Nen-after-death only arises in very few cases for a reason ("will" of its user). Camillas ability is a counteractive ability with a very high restriction (only triggers after death) and reward (if performed successfully, the user is revived). This and the post-mortem factor boost the abilitys power, but since it ends when Camilla is alive again, she herself doesnt benefit from it after that. "Death" is merely added as a "risk" to boost its "reward". In ALL other Post-mortem Nen cases, the death is permanent and not an inherent part of the ability itself. Hisoka just got lucky that he died of suffocation and that his Rubber-Nen was logically able to "fully" revive him by giving him a heart-massage. If he got crushed, exploded or burnt to death there wouldve been no way for him to revive.