Dear Dr Aklujkar,
Cognisant as I am of your expertise, I must respectfully disagree. In the context of the Pratyabhijñā philosophy being expounded by Abhinavagupta here, the idea is that the body mind etc., which are clearly objects of awareness, lose their separate objectivity in this
turyā state, becoming expressions of awareness itself (
tadā bodha-svarūpīkṛtaṃ tad-rasānuviddham eva śūnyādi-dehāntam avabhāti, further on in the passage), not separate from it. So this is not the
turyā of other schools (=
samādhi), because a complete withdrawal from the objects of cognition is here called
turyātīta. In the
turyā state under discussion, it is specifically the objectivity of the objects of consciousness that falls away, not their appearance within consciousness -- but he specifies that the impressions (
sa.mskāra) of objectivity remain.
With regard to your second point, the
Rasa-ratna-samuccaya (5.11) citation (thank you for that!) I think shows that
vedha can indeed mean transmute; so what we have in the Abhinavagupta passage is three stages in the process (in which the agent is
ahambhāva or
svātantryarūpa-bodha). The first is denoted by
vidh-, permeate, infuse, but also transmute; the second,
abhini+viś, immerse completely (now dehādi have become like gold); the third,
jīrṇa, in which all trace of objectivity (the
sa.mskāras referred to above) are "worn away" or the gold is "digested" by the mercury in the metaphor. (This is now
turyātīta-daśā). Thus the mercury preparation (
siddha-rasa) changes the base metal to gold, then with prolonged exposure eats away that pure gold itself, since Abhinava wants no trace of objectivity left in this process. A nice (if surprising) metaphor, since the idea of pure gold triggers our
rāga, and therefore must be dissolved, leaving only the dynamism of consciousness itself.
Torella (1994) supports my reading in his summary paraphrase of this passage: