SB 1.9 - Bhīṣma attains Kṛṣṇa
Merging his mind, speech, sight and actions in Kṛṣṇa, Bhīṣma became silent and his breathing stopped. Bhīṣma merged his self into thinking of the Lord and his mind into remembering Kṛṣṇa’s different activities. He chanted the glories of the Lord, and by his sight he saw the Lord personally present before him, and thus all his activities became concentrated upon the Lord without deviation. This stage attained by Bhīṣma is called nirvikalpa-samādhi. By practicing any one or all of the nine methods of devotional service under the guidance of an expert devotee, one can achieve the same perfection as Bhīṣma. For Bhīṣma the Lord was personally present, but we can use the sound incarnations of the Lord in the form of hearing from Bhagavad gītā and Śrīmad Bhāgavatam and die like Bhīṣma which is the perfection of human life.
Knowing that Bhīṣma had merged into the unlimited eternity of the Supreme Absolute, all present there became silent like birds at the end of the day. Viśvanātha Cakravartī says that it was the ignorant, who were like birds who think that day has been destroyed at the approach of evening, thought that Bhīṣma had attained the Brahman and became silent. Bhīṣma had attained his cherished form of Kṛṣṇa as the charioteer. Just as the day is not destroyed at the approach of evening but it still exists, for after twelve hours daylight appears again, Bhīṣma at that very moment in an invisible form fights on the ground with Kṛṣṇa holding the chariot wheel in His hand. And in a future appearance of Kṛṣṇa, Bhīṣma would also appear with Him.
The living beings are parts and parcels of the Lord, and therefore they are eternally related with Him as the servitor and the served. The conditioned souls in the material world have separated themselves from the whole, but the eternally liberated are always integrated. One can attain the Supreme thru jñāna, yoga or bhakti. The jñānīs and yogīs enter into the impersonal rays of the Supreme but the bhaktas enter the spiritual planets of Vaikuṇṭhas. Bhīṣma entered the spiritual realm in one of the Vaikuṇṭha planets where the Lord in His eternal form of Pārtha-sārathi predominates. One cannot explain that Bhīṣma merged into the Brahman since Bhīṣma did not desire liberation and it would be improper for the Lord to give undesired results forcibly. By giving him something devoid of his goal, Kṛṣṇa would be cheating His eternal associate Bhīṣma of prema.