Is a believer who dies during or after heart surgery considered a martyr, and will his body remain preserved in the grave, and is the softness of his limbs during ghusl a sign of his faith?

When a believer dies, they are praised with good words, prayers are made for them, and good is hoped for them, because the Prophet, peace and blessings be upon him, said: "Whoever you praise with good, Paradise becomes obligatory for him." Describing someone as a martyr is limited to those who have been mentioned in the Ahadith, with the possibility that Allah may, out of His grace, join him with the martyrs. As for his body not decomposing, there is no evidence for that. Signs of his death upon faith, such as the brightness of his face and the softness of his limbs, remain among the signs of goodness.