Looking at the issue from one angle, since the bodies of living things have been created in a way that once the soul leaves the body, in accordance to the laws of nature, the body begins to smell, rot and eventually decomposes completely. Obviously, with this in mind it becomes difficult to digest or accept that a corpse can remain intact after the passing of many years.
However, one must also note that since Allāh (swt) is All-Powerful over His creation, such an incident should not be so difficult to comprehend, and one should avoid labeling it as rationally impossible, or completely uncommon. This general rule (that bodies decompose) is also subject to exceptions, hence through the permission of God, there can be factors that stop bodies from decomposing or rotting, for instance; mummification can cause a body to remain intact and unharmed, this is something proven through experience for over thousands of years. Similarly, should Allāh (swt) wish to establish a point, He can will for a person to become lifeless for many years whilst preserving their body from deterioration, then for a second time blow [their] soul back in to the body, such an example can be found in the story of the Holy Qur'ān regarding Prophet ʻUzayr (as).
Also, it is mentioned in narrations that the body of someone who performs the Friday ghusl will not decay.  There are countless accounts of such events, whether they are narrated from mouth to mouth, or through news sources, where the bodies of believers after being dug up were found fragrant and intact.
Therefore, although the decomposing of a body after death is a natural occurrence, which is what happened to most of the martyrs’ bodies, if the body of a martyr is found to be intact and not have deteriorated, this shouldn’t be seen as something unfathomable since it is possible that one of the above factors may have played a role [in preserving the body].
 Aal-Imran:26; Tahrim:8.
 “Or like him who came upon a township as it lay fallen on its trellises. He said," How will Allah revive this after its death?!" So Allah made him die for a hundred years, then He resurrected him. He said," How long have you remained?" Said he," I have remained a day or part of a day." He said," Rather you have remained a hundred years. Now look at your food and drink which have not rotted! Then look at your donkey! [This was done] that We may make you a sign for mankind. And look at the bones, how We arrange them and then clothe them with flesh!" When it became evident to him, he said," I know that Allah has power over all things”
 Friday ghusl and the body not disintegrating in the grave, 4156 (site: 4583).