How do we read him? It is not such an easy question to answer.
From the perspective of Mahāyāna hermeneutics he needs to be read in the context of the main Prajñāpāramitā Sūtras, and the Samādhirāja Sūtra (Candrapradīpa Sūtra), the Kāśyapaparivarta Sūtra (Ratnakūṭa Sūtra), and so on. All of the outstanding Indian mādhyamikas such as Candrakīrti, Śāntideva, Śāntarakṣita, Kamalaśīla, Vimalamitra, Maitrīpa, Atīśa, etc., backed their readings of Nāgārjuna with references to these sūtras.
What worries me about that interpretation is the importance Atisha holds to the Gelugpa's, who are ostensibly a continuation of the Kadampa tradition, and the very great weight he places on ethics.
The Gelugpas don't have a monopoly on Atīśa.
Ethics are obviously extremely important, as is extensive solitary retreat practice, and a life of voluntary simplicity. There isn't going to be any meaningful, sustainable prajñā without śīla and samādhi. And this does indeed need to be emphasized.
I would need to see other translations, but the line "the very finding of nothing (there) is the ultimate (truth)" probably does not imply that the relative disappears or is ultimately nothing. I think that it is far more likely that this means "the very finding of nothing [truly existent] there is the ultimate truth."
The Tibetan is:
ma rnyed pa nyid don dam yin
ma rnyed pa (not finding) nyid (the very) don dam (ultimate) yin (is)
the very not finding is the ultimate
In any case, that would be how the Gelugpa's would present it.
Well, not everyone agrees that a pot is still a pot and a pillar is still a pillar.... But this has been debated for hundreds of years.
All the best,