Is emergence the only avenue to follow in order to successfully short-cirquit full reductionist explanations?
What other recourse does one have to avoid full-fledged reductionism without risking back-tracking to some sense of essentialism?
It depends how much goes into the emergent properties as regards the kind of causal power (if any) they possess. I'm going to take part of an argument from J. Kim. It doesn't represent his full view but the premises are relevant, I think, to what you are asking.
(1) Emergent mental properties are real properties (the thesis of emergent realism).
(2) To be a real property is to have causal powers ('Alexander's Dictum').
(3) Emergent mental properties are irreducible (the irreducibility thesis).
(4) To be an irreducible property, is to be a genuinely new addition to the ontology of the world (the ontology thesis).
(5) To be an irreducible real property, is to have new and irreducible causal powers. (From 2 and 4.)
(Cited in more complete form in Achim Stephan, 'Armchair Arguments against Emergentism', Erkenntnis (1975-), Vol. 46, No. 3 (May, 1997), 305-314 : 308.Also see Kim reference below.
The question and the problem are : do emergent properties have new and irreducible causal powers ? If they do, then this is one argument against reductionism. If they don't then this argument against reductionism fails but another might succeed. Whether and which if any emergent properties have new and irreducible causal powers seem not to be a philosophical but empirical issues.
Kim, J.: 1993b, 'The Nonreductivist's Troubles with Mental Causation', in J. Heil and A. Mele (eds.), Mental Causation, Clarendon Press, Oxford, 189-210; reprinted in J. Kim: 1993, Supervenience and Mind, Cambridge University Press, Cambridge, 36-357.
Stephan, Achim, 'Armchair Arguments against Emergentism', Erkenntnis (1975-), Vol. 46, No. 3 (May, 1997), 305-314.
"Reductionism, Emergence and Levels of Reality: The Importance of Being Borderline" by Sergio Chibbaro, Lamberto Rondoni, and Angelo Vulpiani is particularly good with issues of emergence, reductionism and essentialism.
Like others I struggle with your use the of the words.
I would use the term 'emergence' to mean the opposite of 'reduction' such that anything that is emergent can be reduced and anything that can be reduced is emergent. So for me a reductionist explanation is an explanation in terms of emergence.
Holism is the opposite of reductionism as a method but if we keep going long enough we end up in the same place, (viz. the 'world-as-a-whole), so in the end the difference of approach is not metaphysically important.
Which only goes to show that these words may be used in various ways.
Practical emergentism, is compatible philosophically with reductionism. Reductionism must hit problems in ability to make predictions, based on the limits of total matter and energy in the universe and what data could be held and computed. Non linear dynamics mean the universe can only fully compute a single timeline of everything in it. The multiverse may be a computation of all possible initial conditions and timelines: https://phys.org/news/2014-12-universe-dimensions.html
Emergentism, such as predicting behaviour based on psycology, can offer huge shortcuts on computation for predicting outcomes. This treats an explanatory layer as supervening on a more fundamental one, while accepting that it is in principle reducible.
Another example is Multi Level Selection. Group Selection is problematic, because it implies that the new group-unit can become more fundamental than it's constituent genes. MLS resolves this by proposing additional explanatory order, which does not.
When we look at humans, we see a future of digitally uploading and otherwise seeming obviations of the gene. But the gene is actually a record of adaption to niche, a kind of timeline of being. We can never create a digital mind 'from nothing', it must be attached to such a timeline, in the same way we need exposure to culture as well as genes. Additional layers of order occur, but never supercede previous ones. I am thinking of Deutsche's description of understanding genetics as crucial to understanding The Fabric Of Reality.
We expect simplicity and elegance to the order of the universe, as shown by the increasing unification of fields and expectation of a unified field theory. Many expect a unified substance https://en.m.wikipedia.org/wiki/Digital_physics#Wheeler.27s_.22it_from_bit.22 Reductionism in this context is really saying, we expect a timeline that goes from simple to complex.
Do we also need holism? Yes, anc again it is compatible. In that early simplicity, all particles were probably entangled. The emergeging idea of an axiom of purification, suggests the arrow of time is in the direction of increased mixing of initially pure states, which means a particle cannot be fully accounted for without reference to all previously entangled partners.
My impression is that this can picture all possible futures as part of a multidimensional surface. So then you think, why do you subjectively experience just this one worldline? Just like a fundamental particle, in this picture we in fact experience all possible worldlines, 'seperated' by 6 of the dimensions being rolled up (ie having limited extent into our universe).
It is not a dichotomy. Reductionism and emergentism can both be essential to a working understanding of, and creation of a meaningful model of, our universe and wider reality.