In biology, strategic, long-term purpose is mandatory - intelligence is useful in some situations, but is subordinate to purpose and coherence. Therefore a society or person lacking purpose is en route to extinction.
Short-term motivation turns-out to be dependent upon long-term strategic purpose. In other words, where purpose is lacking, motivation is headed for collapse as well.
This happens because without purpose there is no cohesion - because there is nothing to cohere-around.
And without cohesion then short-term, tactical motivations (including basic ones like hunger, safety, sex) dissociate and start to erode by some mixture of 'entropy' (the natural tendency of complex things to accumulate damage) plus mutual conflict, encouraged by natural selection operating faster and more powerfully on components than on wholes.
In sum, lack of high-level organizing purpose both passively allows and actively imposes the destruction of all forms of lower-level motivation.
Therefore, when a human society loses strategic purpose, it will fall to pieces. Purpose just is essential. Some people suppose that society can get-by or at least continue without an overall purpose on the basis of smaller scale, individual motivations - for example that when the purpose deriving from religion has gone, then the smaller scale motivations of smaller scale units such as government, law, the educational system and heal services will continue; there is also the assumption that when 'top-down' religion is removed then individual spirituality will take-over.
Not so - except as a very temporary lag-phase phenomenon: all these lower level forms of motivation will begin to self-destruct as soon as overall purpose is missing.
So what provides overall purpose? The answer is religion - or, in the immediate aftermath of loss of religion some societies found a temporary purpose in nationalism, although nationalistic fervour has never lasted with sufficient strength for more than a generation...
So: religion is needed for purpose - and without purpose there will be extinction.
Plus - not all religions do, in practice, provide national purpose - so the choice is limited.
But the fact is that if The West does not find religion - and thereby by, and by no other means, recover purpose - it will become extinct.
One way or another.
Note: 'Extinction' for The West includes being taken-over by another society which has an effectively purpose-giving religion; hence involving a purpose being imposed on The West group by another group, from externally. Indeed, all genuine purpose must, in practice, be external; in order to be effective and sustainable. Presumably, The West will continue to collapse/ destroy itself (due to lack of religion/ purpose) until this happens either overall, or by piecemeal conquest/ colonization. On present trends, this seems like the most probable scenario.