Buddhists use cremation. The bones of Buddha are also not here.
In fact, most of the pharohs are not available to us because of the salubrious practice of the British, who burned mummies to fuel their locomotives.
Mark Twain recounted an train engineer calling for more power:
"These plebians don't burn worth a cent! Throw on a king!"
To answer both your posts. The biblical account is that soldiers guarded the tomb of Christ. But no matter who guarded it they had everything to lose if they permitted the theft of Jesus' bones.
Re: the bones of Buddha and mummies. Even cremation will not burn away all bone matter. Especially cremation not done in a commercial crematory. The cremains will contain bits of bone and of course there will be ash. So evidence of a body does remain. Also cremation was not a custom for body disposal in the ancient Middle East.
PS. I love the Mark Twain quote. Thanks for the laugh.