Saññāviññāṇasaṅkhayā seems only found once in the suttas, in SN 1.2. SN 1.2 is addressed to a glorious deva, who was obviously not knowledgeable of the Buddha’s teachings. The words “saññāviññāṇa” may have had a different meaning to the deva, compared to its use in the Buddha’s teachings. For example, it is often asserted among Buddhists the word “viññāṇa” means “divided knowing”, which seems to be a Hindu definition. Also, according to a scholar:
Even though the Sanskrit term vijñāna (which in the Upaniṣads designates consciousness as an abiding characteristic of the self) is adopted by the Buddhists as an appropriate designation for consciousness, the interpretations found in the Nikāyas and the early Abhidharma deny its immutability and instead regard it as indistinct from perceptual cognition.
Mind in Indian Buddhist Philosophy (Stanford Encyclopedia of Philosophy)
In conclusion, based on the above scholarship, my general impression is, for devas, consciousness was often regarded as permanent & also distinct/separate from perception (contrary to MN 43, which says consciousness & perception are ‘conjoined’). MN 37 is an example of Maha Moggallana scolding Sakka King Of The Devas for neglecting/forgetting the Buddha’s teaching of impermanence. Therefore, the teaching of the Buddha in SN 1.2 may have been a specific individualized teaching for that deva and is not a teaching to be taken seriously or literally by Buddhists. Here, in SN 1.2, the Buddha may have been hinting to the deva consciousness is impermanent & perception is not separable/distinct from consciousness. We can also note there is no mention the glorious deva delighted in the Buddha’s answer.
Also, since the word ‘nirodha’ is found in SN 1.2, I doubt it can be regarded as synonymous with ‘saṅkhaya’ because for the Buddha consciousness, perception & feeling are ‘conjoined’ (MN 43). This is more evidence the term “saññāviññāṇa” was specifically coined for the deva in SN 1.2. In summary, if saññāviññāṇasaṅkhaya was synonymous of saññāvedayitanirodha then the word “vedana” or “vedayita” would have been included in the compound “saññāviññāṇasaṅkhaya”. 
With the ending of relish for rebirth,
Nandībhavaparikkhayā,
the finishing of perception and consciousness,
Saññāviññāṇasaṅkhayā;
and the cessation and stilling of feelings:
Vedanānaṁ nirodhā upasamā,
that, sir, is how I understand liberation,
Evaṁ khvāhaṁ āvuso jānāmi;
emancipation, and seclusion for sentient beings.
Sattānaṁ nimokkhaṁ pamokkhaṁ vivekan”ti.SN 1.2