I don't know the answers as to what to do in the case of losing all molars, but there are implants made from more biocompatible material than titanium!
http://www.integrativedentalmedicine.com/titaniumcorrosion.html

Here is a biocompatible metal free alternative:
http://www.integrativedentalmedicine.com/metalfreeimplantology.html

Dentures maybe your only option in the case of losing so many teeth, but you'd need to discuss this with a biologic dentist to see what can be done in such a case.