It is worth noting that in Christian theology, heaven is only reached after death, and both going there early and sending people there early are explicitly forbidden.

While an infinite duration of bliss has very high utility, that utility must be finite, since infinite utility anywhere causes things to go awry when handling small probabilities of getting that utility. It is also not the only term in a human utility function; living as a non-wirehead for awhile to collect other types of utilons and then getting wireheaded is better than getting wireheaded immediately. Therefore, it seems like the sensible thing for a FAI to do is to offer wireheading as an option, but not to force the issue except in cases of imminent death.