Reliability is not the issue. If it's reiable enough for flying an approach, it's reliable enough for flying the missed. If it's unreliable, then why allow approaches in the first place? In the US, we're flying precision approaches using GPS, every day, onshore and offshore, fixed and rotary wing, including airliners. i understand that other countries distrust the US government, and I don't blame them, but allowing GPS approaches but not allowing its use for the missed simply makes no sense to me.
Everyone recognizes the need for a backup system, but maintaining thousands of navaids all over the US is very, very expensive, and it's cheaper to use enhanced LORAN for the backup than maintaining, and soon replacing, all those aging, obsolete navaids.