All living things die. I will die. What are some sustainable options for handling dead bodies?
I know about two different studies that investigated which funeral method has the smallest environmental impact. I will base my answer on the most recent study and then shortly discuss the differences with the other one.
In this report drawn up by the Dutch research institution TNO in 2011 two alternatives are mentioned that are have a lower environmental impact compared to traditional burials or cremation.
Resomation is a patented process in which a body is broken down into its chemical components by placing it into a mixture of water and lye and then heating it at high pressure. This will dissolve the soft tissue and make the bones porous, so they can be crushed afterwards. The resulting "ash" can then be returned to the next of kin.
The advantage is that metals or toxic chemicals in the body (e.g. mercury used in tooth fillings) can be separated and this process reduces emissions of greenhouse gases by approximately 35% compared to cremation. AFAIK it is legal only in some states in the US and Canada.
During cryomation a body is frozen solid by immersing it into liquid nitrogen. Then vibration or pressure is used to shatter the now brittle body. The remains are then placed in a vacuum and turned to powder. This powder can then be buried for further decomposition.
As with resomation, the benefits are lower CO2 and toxic emissions and the possibility to separate metals. AFAIK cryomation is legal only in Sweden, Scotland and South Korea.
The results of the TNO study however are different compared to an earlier Dutch study done by researchers of Delft University of Technology in 2005. Sadly I have only been able to find references to the 2005 study and not the study report itself, but this article (in Dutch) discusses the differences between the two studies.
In the Delft University study burial, cremation and resomation were considered to have a more or less equivalent environmental impact, but cryomation was found to have a big impact. The difference between the two studies is said to be caused by different weighing factors. Also the TNO study includes recycling of metals and toxic chemicals (not included in the Delft University study), but it also uses a relatively big impact factor (perhaps bigger than necessary?) for ground use in burials. Note that the results may not apply to other countries, since they are based on funeral regulations and customs in the Netherlands (e.g. coffin required for burials)
There are 3 other options that are sometimes mentioned as being more sustainable (than burial and cremation), but that AFAIK have never been researched as how sustainable they really are:
Sky burial: a traditional Tibetan and Mongolian custom where a body is taken to a mountain top, cut into pieces and then fed to vultures or other birds of prey.
Sea burial: disposing a body into the sea.
Natural burial a.k.a. green burial: like a traditional burial, but then with a biodegradable coffin or shroud, allowing the body to decompose quickly.
One final note; the Delft University study I mentioned earlier also found that the biggest environmental impact of funerals comes from the people who are driving (or flying?) there to attend (source: this article in Dutch):
Dogs and cat food.
It has to be domestic animal (and not pigs, for example) because you don't want to put human flesh in a cycle (it could cause a equivalent of mad cow disease)
The logistic need for this method is close to zero. The local butcher can totally deal with the job.
Now, I admit, this is an answer to the second part of the question: What are some sustainable options for handling dead bodies?
It hardly qualify as funeral. Because funeral is mostly about showing to the livings that a body is not to be treated as raw matter.