Creating happy immortals is way simpler than people give it credit for. The barrier people make for themselves is insisting that an immortal being would need to have the psychology of an adolescent human being.
Also this:
http://tvtropes.org/pmwiki/pmwiki.ph...reverIsAwesome
As for the issue of Bernkastel and Rika, I thought it was pretty clear cut that Bernkastel is an offshoot of Rika's negative futures. This doesn't cheapen Higurashi's ending in any way, as Rei drives home the point that we are not gods who are supposed to make everything perfect in all ways. We've gotta give and take and be grateful for what we did get. I imagine this lesson will be extended to Ange too.