Marga means the way, the skilful arrangement. According to the proper conclusions being presented, they had a proper (sam) situation (stham) within the Lord’s manifested and unmanifested pastimes in a spiritual condition. There was however a destruction of the external conditions. Svah refers to Krsna’s spiritual abode. It is said:

na va idam rajarsi-varya citram
bhavatsu krsnam samanuvratesu
ye ’dhyasanam raja-kirita-justam
sadyo jahur bhagavat-parsva-kamah

O best of kings! It is not surprising that those desiring to associate with the Lord, born in the Pandava family and devoted solely to Krsna, immediately gave up the royal throne served by kings' crowns. SB 1.19.20

sampadah kratavo loka mahisi bhrataro mahi
jambudvipadhipatyam ca yasas ca tri-divam gatam

kim te kamah sura-sparha mukunda-manaso dvijah
adhijahrur mudam rajnah ksudhitasya yathetare

O brahmana! He had all wealth, sacrifices, planets, queens, brothers, the earth, lordship over Jambu-dvipa, and fame in Svarga, desirable even for the devatas. Did these things give joy to the king, whose mind was only fixed on Mukunda without deviation and nothing else? SB 1.12.5-6

Though only Yudhisthira is mentioned, the same applies to all the Pandavas. All five brothers made up their minds to attain Krsna’s abode. Nibhrtatma means that their thinking was not revealed to others.